As others have said, it all depends on how quickly you get cold while diving. Even warm water pulls heat out of us. Some have a greater tolerance for this than others.
For myself, most of my warm water dives have been in Maui. Even when the wtaer there has been 80 F (or warmer), I've always found a shorty to be inadequate. A 3 mm full suit is usually alright for the first dive, but during the second dive I start to feel a bit chilly (especially during night dives). If there's a third dive, I always feel somewhat cold. That's why I've bought a 5 mm wet suit (a Pinnacle Fusion). I'll be going back to Maui in February and in August, and I'm really looking forward to being comfortable during every dive.
As far as being too warm on the boat before the first dive and suring the surface interval(s), I've found it best to be partially "undressed" -- i.e., keeping my chest and arms out of the suit until just before putting on all the dive equipment. (In fact, I've even done this while using a 3 mm full suit -- most people feel much warmer in air than in water of the same temperature.) And if I feel a bit too warm during a dive, I've used the old "pull the suit away from the neck in order to let some water in" trick. Works every time.
In any case, wear a wet suit that works best for you. Comfort is much more important than style here.
