I can and will run at any level, however:
Epic is, in my opinion, just stupid. There are better homebrew methods of dealing with 21st and higher.
I love the 5th and above; survivability, power, yet still vulnerable to all manner of nasty DM tricks.
The key to high level play is to restrict, *HEAVILY*, what the players have access to. Primordia, which is my own campaign world, has a definite and specific list of sources available as well as a lot of info on what the players cannot not have. This includes a list of forbidden spells, feats, sources, a maximum of one prestige class that, without excellent roleplaying, must be maxed out before taking any other class levels, etc. Although it seems like a ton of info, the handout is only about 15 pages long (which includes regional info, economic background, and a lot of other fluff) and my players really seem to enjoy the game.