depends on the material. A lycra jammer will fade just as fast as a lycra traditional speedo. There is no major advantage to jammers vs traditional. Lycra is the most popular material for training. Once you step up to higher end materials you might find some advantage (FS2's). Between the compression and the wicking material there is a difference.

You also have to look into how your body reacts to it. I know many many distance swimmers who dont like full body suits or jammers because they are not as breathable as speedos and overheat. Overheating causes a chain of events which equals crappy swimming.

training wise here is what I would recommend, a traditional speedo with a mesh drag suit. The mesh suit will last forever, even if your speedo starts to fade a bit no one will know . Then determine what you want to race in. Jammers are becoming more popular (even more so with 18 and under) because people get a little shy in speedos I guess?? Who knows.