For our first trip to Hawaii, our children are saying: Maui. And our friends who have traveled and/or lived there are saying that in January the best part of the island to stay in is the southwest. We'd like to rent a house on or within a short walk to the beach and do not want to stay in a large condo/resort development. Availability seems better in Kihei, but I wonder if the beaches are better, and the area is quieter further south in Wailea. Then again, maybe it's the opposite.
Any help would be appreciated.

Perhaps quieter in Wailea; but the beaches are fine from Kihei down to Perouse Bay, just different. Hope you'll be visiting a variety of them.
Most of the Kihei properties near the ocean are condos; houses will be back from the beach (up the hill in Kihei), and will entail walking (or driving and parking). "Oceanfront" Kihei will mostly mean crossing the street to the Kamaole beach parks (I, II, III).
Can't think of houses in Wailea that are beachfront; but there are many "villas" and condos "steps" from the beach.

Well, those two areas are apples and oranges. Kehei has more of a southern California pacific coast highway vibe to it. Wailea has more of a Beverly Hills on the beach vibe. And lodging prices vary accordingly. It depends on which vibe appeals to you the most.

BTW, you might try the MAkena Surf condos; they're beachfront, and a relatively smaller development.

We have stayed in both areas. In Kihei at the Maalaea Surf Resort in building D. http://www.maalaeasurfresort.com/ which is right on the beach. It is a condo complex but only 2 stories high. Most of the other condos in this area are high rises. In Wailea we stayed at Napili Shores which is not on the beach but within walking distance. Very nice 1-2 story condo's with clean grounds and swimming pools. Both condos are reasonably priced with parking for no extra charge.
Monterey Bob had it right when he said that the two areas are complete opposites.

Napili shores is not in Wailea

montereybob summed it up nicely. Kihei is cheaper by far, and can be a bit more like a college spring break atmosphere. Wailea is far more expensive and upscale, more like a well-moneyed L.A. atmosphere.

You might try looking into Kapalua (on the northwestern side) or Makena, just south of Wailea, for something in between Kihei and Wailea. Both of those areas have a few B&Bs, rental properties, and smaller hotels very near beaches if you don't want the large resort experience.

BTW, you might want to read up on the Maalaea area; it is very windy, and there's agriculture drainage that enters the bay there.

You folks are great! Thanks so much for the information.
I'll re-start digging around.
Keep those suggestions coming!

There is a difference between North and South Kihei in terms of quality of beaches and neighborhood. The beaches south of the Cove Park are great if you do choose Kihei. Also, Kihei is definitely more kid friendly then Wailea.

Decision made- Wailea it is!
My thanks to all you helpers....

My best advice: Bag artificial/mega resort Wailea and get to north of Lahaina - at Kapalua or Napili.

Beware of Kapalua/Napili in January, as you can get an extended period of rain and wind during the winter, as we did once (8 days). Since then, we have returned to Wailea and Makena - and I found that seeing the odd cactus around there, was somewhat reassuring, after our 8 days in Kapalua.
Mind you, we still do day trips to the Kapalua area, as it is a great spot.

agree with kanunu, you'll most likely have rain and wind in January. I'd go with Wailea and drive into Ka'anapali now and then. The beaches are better in Wailea and south of there. (Big Beach, Little Beach)