Macargo... ? LOL. Have fun against the Admin with Entei.
I would want to Nuzlocke Colosseum because it'd be a fresh take on the game, and truly a challenge, IMO. I'm sure I'll be throwing my wii out the window by the time I beat the Admin I mentioned above, but... yeah.
On that note, I personally think that Admin is the hardest of them; if you're trying to catch Entei. At that point in the game, you don't really have anything that doesn't die to Fire, Rock, and Ground all at once, all the while killing everything but Entei on his team, and then trying to catch it as it Fire Blasts you to hell. ... Yep. Good times. DX
Entei isn't even any good, either... Damn GSC legends being so rare when Colosseum came out! DX