Most Helpful Guy
It really doesn't matter which one you get. The best ones that fit big boobs are ones with built in cups. You can always count on finding the right bathing suit when you ask girls for advice. I'm not good with answering this question.
Most Helpful Girl
If possible, try to find bathing suits that are made for bust size, so that they have underwire for that support. They may be a little more expensive if it's worth it. Otherwise, chose bathers that are full cupped, nothing with push up padding!! Anything with frills makes the bust look bigger, so stick to basic patterns and colours. You can still absolutely wear bikinis if you want too but just make sure they are specific cup size so you don't stick out or fall out (and they support you and give you lift!). Shopping for bathers with a big bust is hard, I've been there and done that but you will find a perfect swimsuit that fits well. It just takes a while (and possibly a bit more money). Good luck!