Anyone tried 30 day fitness challenges that has a favorite?

YouHadMyCuriosity

I finally looked up all the 30 day fitness challenges I've seen periodically talked about on the community boards, and I want to do one (or two) as an extra supplement to what I'm already doing. Anyone have any favorites?

I'm thinking about either doing the tricep dip or lunge one (since these two moves are somewhat lacking from what I've been doing recently), but so many of them sound great!

If you've done them before, tell me which one you liked the most, or got the most out of!

If you haven't, or have no idea what I'm talking about, look up 30dayfitnesschallenges.com- they have some great stuff!