1: Tough decision, but it would probably be the Nether. There's more I could do there, and I wouldn't have to worry about falling into the Void.
2: A snowy forest. I haven't seen one yet! :-)
3: Oh, gee, that really depends on if I built a portal or not before I died. If I did, sure. If I didn't, then I would probably just leave that world and start a new one, since all my creations would be stuck in the Overworld, and I stuck in the Nether.
4: MOOSHROOM! I love mooshrooms. Plus, I would never have to worry about getting attacked by hostile mobs, since I would live on a mushroom island.
5: Oh, gosh, I really wouldn't want to be either. But I think if I was forced to pick, I would probably pick the Wither. If Herobrine existed, he would constantly be bothering people. The Wither only bothers the people who are crazy enough to summon it.
6: Black! (like a ninja... :P)
7: I would probably beat up Herobrine. Since I would HAVE to fight the Wither eventually, it would be a once-in-a-lifetime oppurtunity. But of course, Herobrine would have to exist for me to do that. And I don't think he does.
8: Kind of confusing. Gold, I guess?
9: DISNEY WORLD! (if that IS possible...
10: ICE CREAM OR PEANUT BUTTER!