I haven't really thought about this much, but I'll contribute mine just off the top of my head..

And I'll start with worst, so this post doesn't end on a depressing note.

Worst:
~Being jolted by a friend's suicide
~Having to break someone's heart.
~Watching my best friend slowly ruin herself

Best:
~Going backpacking this summer, challenging and pushing my limits yada yada yada
~Spending two days by myself in the wild with nothing to do but contemplate life.
~Becoming first clarinet in my band (and orchestra) yeeeeeeee haw! Domination!
~That's all I can think of right now.