If you're not in it to win it, by all means skip the suit. But if you have even the mildest aspirations to greatness (or just want a boost), you're going to want a wetsuit. Today's models are slightly buoyant and so lift you into an ideal swimming position, which makes your stroke more efficient.
We gave the Roka Maverick Elite, one of the "entry-level" wetsuits (for a bargain $450) a test swim and found its a buoyancy to be something of revelation. And while we ditched the suit for an August triathlon (which was in 78-degree water), every participant in front of us coming out of the lake – and we do mean everyone – still had theirs on on. A suit is even more of an advantage as the weather gets colder: According to USA Triathlon, the number of competing triathletes in the U.S. drops from a peak of 300,000 in the summer to a spare 50,000 by October. The course is all yours! [$450; rokasports.com]