You don't really get the full experience of what a build is like until after level 22-25 or so, so it's difficult to mess around with different characters when they are all level 15.
I recommend focusing on a single character for now. In addition to that, I recommend making another character and using him as your 'skip the fun.' That character instantly becomes level 30 and you get some gold, but he doesn't gain experience. The neat thing about this is that you can respec that character's stats for no penalty whenever you feel like it. That way, you can still get the experience of those classes ahead of time.
If you like one of those skip the fun classes, you could develop it more on your alt or your main if you retire.