I think it's great to fly into Hilo (and back - out of Kona) - and if the plane goes down the east side of Big Island into Hilo - you get a beautiful view of the Waipo Valley and all.

It really all depends on how much you like to drive and see beautiful scenery. The scenic drive from Hilo - via the Volcano - over to Kona - driving time - is a couple of hours - maybe more - depending on how much you want to stop, see the sights, etc.

I personally would recommend you stay a couple of nights up at either the Volcano House at the visitor's center - or in the nearby Volcano Village - in a rain forest. Here is one place - the Volcano Village Lodge - which I have been to and my wife and mother in law loved staying there. http://www.emmaspencerliving.com/volcano-village-lodge/

And even if you only drive from Hilo over to Kona via the Volcano route - once you get to the Kona side (you might stay at a resort north of Kona if you are sensitive to VOG, etc) - you can easily drive up to Waimea town and further over to the Waipo Valley - and/or to the top of the island at Haiwa if you want to.

And another way to see some of the Big Island is to take a helicopter flight. We did one up to the North side - which has 3 of the longest free falling waterfalls in the world and also had a great view of the Waipo Valley - and you can also fly over the Volcano if you choose, and one deluxe option allows you to do both.

It certainly makes some sense to to fly into Hilo and out of Kona. But all it will really save you is the drive from the Kona coast to the Hilo/Volcano area. Since it only takes about 2 to 2 1/2 hours to do that--I wouldn't let that be the deciding factor.

And if you decide to fly into Kona from Honolulu, just take one of the mid morning flights and that would allow you plenty of time to get to Hilo or Volcano (or Kapoho), going through Waimea and along the coast (a gorgeous drive) by mid afternoon. I'd spend 2-3 days in that area--go to Volcano National Park, visit the tide pools in Kapoho, go the the attractions along the coast (Akaka Falls, Hawaiian Tropical Botanic Gardens,Laupahoehoe, etc). If you want to visit Waipio Valley from Hilo, it is about a one hour drive.

Then to get from the Volcano/Hilo area to the west side of the island, I would suggest that you go around the south end of the island, stopping at Punalu'u black sand beach.

As to staying at Waipio, there are a few bed and breakfasts in the area. Here are websites for a couple of them -http://www.waipiowayside.com/
http://www.waianuhea.com/
We've stayed at Waipio Wayside many times and find it quite comfortable.

As far as driving on the Saddle Road, check with your car rental company about their guidelines. They really can't stop you but they can refuse to come help you, if you have any problems. Given the choice of driving along the coast and across the saddle, I would always take the coast (and they do take about the same amount of time). The west end of the road is quite rough and narrow in spots--it is wider and smoother as you approach Hilo.

As to the vog, we go to the island of Hawaii twice a year and always stay in south Kona and the vog has never interfered with anything we have wanted to do. My observation is that it usually is more visible up the slopes of Mauna Loa than on the shore and tends to hang off the coast (which ruins the chance of a green flash at sunset). Here is a good website about the vog issue--http://weather.hawaii.edu/vmap/index.cgi
And you are correct--there are beautiful rentals in south Kona.

If you were thinking of a day trip to north Kohala, that would be easy to do when you are on the Kohala Coast. Take highway 270 from Kawaihae to the Pololu Valley overlook, have lunch in Hawi at either Bamboo Restaurant http://www.bamboorestaurant.info/or Sushi Rock http://sushirockrestaurant.net/, then take highway 250 over the extinct Kohala volcano to highway 60 near Waimea and then back to the coast.

Hope this was helpful.

Saddle Road isn't restricted, just the road up to the observatory on Mauna Kea (the road that goes from the visitors center up the mountain).
Vog varies, but it was visible in Kona yesterday; if your lungs are compromised, you might want to avoid Kailua-Kona and stay farther north (Waikoloa resort area or even farther).
I don't think Volcano House has reopened yet; you might want to check the website for updates on their remodel.

For me it really comes down to your on island plans, and what time your interisland flights will be.

For an 8 night stay, we chose to fly into Kona, stay in Hawi and the Volcano. Our last day was a leisurely drive back to Kona and a sunset dinner before heading to the airport. It was perfect for our timeline.

With 14 nights ending with 5 or more in Kohala I would consider a few in Kona to exlore that area, then head to Hilo/Volcano and finish up at the conference. For us it is worth changing things up to spend time at a corner of the island rather then making whirlwind day drips with 6 hours of driving.

Best to plan to stay in both Kohala and Volcano, and to fly into one side and out of the other. If you stay west and drive to see Volcano National Park you don't have much time AT the volcano before it's time to hurry back -- and you'd miss any 'red glow' after dark. No need to stay in more than these two locations.

We don't drive distances on Big Island after dark or in rain. This is also the only island where we routinely rent a mid-size or larger car. Distances are greater; you're driving faster; the island seems to have more than the usual number of lolo (impaired) drivers!

I recommend Kohala -- not Kona Town or Captain Cook. (Take the north route. Also, IMO the black sand beaches are not worth the time it takes to view them -- and the sand is coarse! LOL)

why is it best to fly in on one side and fly out the other side?

I personally would recommend you stay a couple of nights up at either the Volcano House at the visitor's center
Closed for renovations until the end of 2012 or longer

I have noticed that the one-way car rental (pick up Hilo, drop off Kona) will cost more than picking up and returning from the same spot, but this would save us having to drive from Kona to/from Hilo twice.
It's only a two hour drive going through Waimea, two and a half going through Ka'u and less than two going over Saddle Road. If money is a concern, book an afternoon flight and return the rental to where you picked it up.

Now that Saddle Road is mostly repaved, I think it's the most scenic route into Hilo. Views of Mauna Kea, Mauna Loa, native flowers and trees, wild life etc.

Two nights in Volcano is more than enough, if you like snorkeling, consider a few nights in Kapoho. VRBO has plenty of rentals right on the tide pools.

I live here so if you need additional information, my email is in my profile.

Aloha

Thank you SO MUCH for the advice and recommendations. I will print this all out.

Based on everyone's recommendations, I think we will have to stay near Volcano National Park for one or two nights (probably Volcano Village Lodge as Volcano House is closed).

A helicopter flight sounds like a fantastic idea. And I never even thought about the scenic aerial views that we would get flying into Hilo and out of Kona! Brilliant!

We love to snorkel (and like to scuba, too, but I am not sure I still can, given my asthma), so Kapoho sounds like a must.

The island sounds incredible--all three roads from Hilo to Kona seem worth doing--how to decide? I am still leaning toward the northern route that goes through Waimea, as we can also do a separate day trip to the Saddle Road while we are staying on the West Coast, and as we can go to Volcano National Park from Hilo. Two weeks doesn't sound like enough now!

I feel I should explain: We would like to minimize driving time because my husband hates to drive, and I am not a skillful or competent driver (even after completing adult driving school, high school driving lessons many many years ago, and additional lessons with friends and family). This is why we are considering flying into Hilo and out of Kona.

I'm not seasoned, only been to the Big Island once but here are my thoughts.

I don't think you really save yourself much driving at all by flying into one and out of the other. Volcano NP is 2 hours from Kona, an hour from Hilo. So, if you visit from Hilo it's 2 hours roundtrip. If you simply visit it on the drive from Kona to Hilo and continue on to Hilo for a few days, it's a 3 hour drive total.

Since you already want to drive the Saddle Road as a day trip, you could drive that to get back to Kona. Or vice versa, Kona to Hilo via Saddle Road, then Hilo to Kona via VNP.

Either way, you are really only saving yourself about an hour of driving if you choose to fly into one city and out the other. For me, that's not worth the extra one-way drop off fee.

And for what it's worth, the flight into Kona is not scenic once you get onto the western side of the island. I was having serious misgivings about Kona when I saw the landscape - very dry, lava and brown grass everywhere. Not at all the tropical landscape I had imagined. Of course, that was just near Kona along the coast - and once we got on the ground and started doing things it didn't matter.

Flying into Hilo usually gives you a very nice view of the island from the air - and you can drive up from the airport up to Akaka Falls in half an hour - and see some of the verdundant area north of Hilo - and then double back to the Volcano area and be there in an hour or so.

Then you eventually make your way over to the Kona side - and fly out from there more easily than returning to Hilo.