divebrasil:
Should I rent a car in maui?
Yes, everything is a drive from the airport to the West side, which is the tourist area.
I noticed there are two airports also
I've always flown into Kahului, the main airport and then drove across the island to either Lahaina or Wailea. Kahului is where the locals live, there's really not much there for tourists, the cruise port is there, things like the Home Depot, Walmart etc.
Some flights do land at the West Maui airport, if you stay in the Lahaina or Kanaapali or Kapalua area it would be a lot closer, but I think the fares are higher. You'll still need a car unless you want to stay close to your hotel. Most of the diveops don't pickup. This summer they started limited public bus service so that's an option for general sightseeing.
But if you plan to dive the best of Maui, the boats leaving from Kihei typically do Molokini and South Maui, the boats from Lahaina typically do Lanai. So to do both you'll drive at least once since it's much quicker to drive to Kihei and sail over to Molokini than it is to sail over to Molokini from Lahaina - or vice-versa. It's a good 35-45 min ride since there's really only one main road that goes north/south along the West Maui coast.
If you plan to take a helicopter ride, you'll also have to drive back near Kahului to the heliport, unless they pick you up with their van. I highly recommend it, you'll see parts of Maui that are almost inaccessible. We hovered about 50' away from a 200' waterfall, flew into the volcano craters and out towards Hana. There's some amazing scenery that you can't see any other way as there's no road encircling Maui.
Where is the best area to stay if we want diving and other kinds of leisure?
Depends on what you want. Anything around Lahaina will be more crowds. Personally I think the area near Whaler's village is the worst, there's a lot of condos/hotels golf courses nearby that add to the congestion.
We stayed north of Lahaina once about 1/2 way between Lahaina and Kapalua, in a quiet condo right on the beach with a 10min drive to Lahaina for everything except the nearby McDonalds. It was pretty nice.
You'll find that more of the activities are based in/near Lahaina. Parasailing, Jetskiing, the sub trip boats, dinner cruises, catamaran sails etc. are mostly based there or nearby in Maalea. Or down in Kihei.
Kapalua a little farther north is a nice area if you're a golfer, but farther from everything else. It's also pricier.
My dive buddy and his family just stayed last month at a condo in Maalea, which is 20min. south of Lahaina, it's quiet in that area. Nice quiet sandy beach 200' from their door, during the week they had it to themselves. A lot of the locals go to the beaches all weekend - I would if I lived there!! But from there you'd be driving to everything except the couple of restaurants in the Maalea pier area, it kind of shuts down at night. The Maui Seaquarium in that area is worth the trip, I read recently that you now can dive in their shark tank.
Lahaina is like a cross between Mission Beach and LaJolla w/o the cliffs. Art galleries, touristy type restaurants - Hard Rock, Forest Gumps etc. - dive ops, t-shirt shops etc. It's just this side of trashy in some areas. North of Lahaina is Whaler's Village, it's the closest thing to a mall on that side of the Maui. Several good restaurants in that area - one was called Auntie Rose's or something similar. Great view of the sunset during dinner.
If you like crowds, stay in one of the big hotel/condo complexes in that area. Or at/around the Sheraton at Black Rock.
Last trip to Maui we stayed south of Kihei in Wailea. The big draw there is the famous golf courses and the Grand Wailea resort - which is super, but expensive$$$. They have an outstanding buffet there though, worth the trip if you're staying nearby. If you're a golfer, play the Blue course, if you're a great golfer, play the Gold. It's pricey though, get discounts on the web or through your booking agent, we saved $50 by going through our condo's front office. And I think it still was $185pp.
We had a newer one br ground-level condo with a view of Molokini from the patio for about $135/nt. It was in a complex with about 30 4-unit buildings with a 1 block walk - on property - down to the beach. The only downside about it was that it was right next to a public beach so always busier. You do want to watch what you leave locked in the car at public beaches on Maui, some of the car rental agents warn you where.
A lot of the condos closer to Kihei are bigger multi-unit buildings, some of them are on right on the water. We liked being a few minutes away from town, it was quiet at night. There's good shorediving in the Wailea area, Wailea Beach, Makena landing, 5caves/5graves are all 10min away. Parking fills up fast so go early.
Wherever you stay on Maui, it's pricey. If this was my first trip to Maui, I'd stay somewhere near but not in Lahaina - maybe just to the south for more of the "Maui" experience. But I'm not a fan of big resort hotels.
my (long) .02