Speedos are great for showing off that physique you worked so hard for. They are also the best swim suits to reduce drag
Jammers are my second choice when it comes to cutting down drag, they are much better than swim trunks but offer less mobility.
Swim trunks are great for parties, beach days, and everything fun, however, they do create a lot of drag and make it harder to swim. I don't recommend them for lap swimming.