Hmm,
Among the purists, I would say the standard is to go starkers under the suit. I guess that makes me a purist
I'm not sure how much difference a bathing costume reduces warmth under the suit, but wedgie prevention is definitely an advantage, and I have a possibly unfounded belief that "going" in your suit when you're out in the water works a little better sans swimsuit.
Among divers I've swum with (is that a word, or did I just invent something?) and have changed with, I'd estimate it's somewhat evenly split between textile wearers and the full monty types, for both guys & gals.
I was glad to see that the Performance Freediving crew got reporter Matt Gutman off to the right start, with an excellent undertowel change technique:
'Human Torpedoes' Race Underwater | Video - ABC News
Some more technique here: [ame="http://youtu.be/q_nOIllGZpE"]How to Surf for Girls : How to Change into Your Wet Suit or Bikini - YouTube[/ame]
For the ladies, taking a jacket off requires development of good towel/blanket skills, or, since in most of Canada & Europe tops aren't a legal requirement for women, in the right environment they can just do the same thing as the guys.
There are a couple of helpful products I'd like to try out once finances permit:
How To Change Into A Wetsuit In A Parking Lot - YouTube ,
or, since the easiest solution to outdoor changing issues, especially when it's cold outside, is to just wear your wetsuit home & change inside:
[ame="http://youtu.be/7kVU1lZYboA"]Surf-fur Water Parka Used in a Car - YouTube[/ame]
The parka looks like it would keep the vehicle seat in much better condition that the garbage bags & plastic sheets I've been using.