Coastline best north or south of San Fran?

Depends entirely on what you like best. North of the GG bridge you have Marin Headlands and Muir Woods (big Coast Redwoods).
South of SF you have Point Montera lighthouse, Half Moon Bay, Pigeon Point lighthouse, Monterey and Big Sur.
What do you want to see?

The coastline is more easily viewed and appreciated SOUTH of San Francisco. Route 1 is spectacular all the way from the city through Half Moon Bay, Santa Cruz, around Monterey Bay, through Monterey, and then the famous stretch south of Monterey through Big Sur and to Morro Bay.
Your trip should depend on how much time you have. Take 1 day for the trip south of San Francisco to Santa Cruz. You can stay in Santa Cruz, a lovely town with reasonably priced accommodations and a wonderful old-fashioned boardwalk/amusement park.
If you have time to spend a day or so in Monterey, then try staying in Pacific Grove and exploring Carmel and old Monterey, including the Aquarium.
From Carmel, plan a day to drive south to Morro Bay. If you wish, add in some time to stay in Cambria and use that location for a visit to Hearst Castle.

We were thinking 10 days maybe 4 south and 6 north

Please clarify: 10 days total? or drive south for 4 days and north for six? If you are splitting the time, reverse it... do the south of San Francisco part in 6 days and the north in 4. You can go to Marin County, the coast of Sonoma County, and some of the wine country easily in the 4 days. Visit Point Reyes, have oysters in Tomales Bay, and sparkling wine in Guerneville.

I'm sorry, but you really need to give us a bit more information and not have us guessing at the details.

How many days in total? Are those days all on the road or do they include stays in cities like San Francisco and Los Angeles? What do you want to see and do along the way?

I can drive from SF to LA in about 6 or 7 hours - a one day trip, so what is it you would like to do and see during all those days?

10 days total, we visited San Fran before so wouldn't need much time there this trip

Probably south as far as Big Sur only also

people are trying to help you but you keep giving one line responses. It is like pulling teeth

When?
How many -- kids/adults?
Some/any details

janisj: It is like pulling teeth

And wisdom teeth at that.

adnil: I'm guessing that all ten days are going to be on the road - correct?

So, do you want to be lying on the beach? drinking your way through the wineries? Any kids on this trip? Are they old enough to go drinking with you or would Disneyland be more appropriate? Will you have a car or is this a trip by bus/train/walking?

My husband and I (50's) renting a convertible wanting to take in the coastal sites with some hiking,when south of San Fran. North of San Fran would visit a couple of wineries and take in several giant redwood forest hikes.

Where are there reasonable motels or a quaint bed and breakfast location?

Sounds like a wonderful trip. There are a lot of cute places to stay up the coast - and still reportedly some cute places in Gualalja - 4? hours north of Sf - where we had a great time loooooong ago - 4 couples - taking over the quaint/old Gualajala Hotel & Bar. http://www.gualala.com/

Loved the sign in the back - by the rest room - which was in another building: "No washing waders in sink."

Seems a few fishermen or duck hunters stay there.

And there are a lot of posts in here about the Big Sur area. Just keep googling away to find what you want.

One place to stop for coffee and the view is Nepenthene - which I think also has some cottages? http://www.nepenthebigsur.com/

Here is one page for lodging around Big Sur - and also - Carmel should have some cute B&B's, etc - so just keep googling: http://www.bigsurcalifornia.org/lodging.html

And here is a good map from that page:

http://www.bigsurcalifornia.org/map.html