After over 11yrs of Martial Arts(judo, karate, and bjj), the only styles I would do are Brazilian Jiu Jitsu and/or Muay Thai. Due to the way we train in BJJ(we practice techniques against 100% resistance while rolling) a blue is pretty much the equivalent to a black belt in another art. Just yesterday I was making a 300lbs bouncer feel like he was a helpless little child.

But of course thats just my opinion based on my experiences