They've all been fun, with mostly good things and just a few bad things about each one. But I think I'd still say elementary and middle school were better, just because they were more stress-free. High school has been fun, but there is just a little more stress involved because your grades start to really count and you really have to make sure you do well in your classes. You have to start thinking about your future and college and whatnot, and it can be overwhelming. Elementary and middle school were a little more carefree. I can't pick between elementary and middle though, because they were both so much fun for me! I guess I could say elementary since it was the easiest and I had the least amount of homework, haha. And since pretty much everyone was friends and there weren't a bunch of cliques and stuff. You could just go up to anyone at recess and play, and the wouldn't judge you. Even though that kind of stuff gets pretty common in middle school (cliques, people being judgmental, etc.), I managed to escape that since I just stayed with my friends and didn't try to hang around the "popular" crowd. I've heard that a lot of people had a horrible time in middle school, but I actually had a lot of fun. I just had really awesome friends, and I loved most of my teachers in middle school too, so that was also what made it good.
I've had a lot of good school years, and I can't possibly pick one, so I'll just pick one from each school. 4th grade was my best year of elementary school, 7th grade was by far the best middle school year, and so far, I think my senior year has been my best high school year (I'm a senior right now). Junior year was pretty good too though.