scarlet is my vote, but dont be dissappointed if you loose some, my bet is you will. i have scarlets, and a couple emeralds which i am not so sure i should have got, but so far so good with them.
I would stick with scarlets. The blue legs are usually cheaper but thats becuase they will pretty much try to take everyone elses shell (snail or crab) and kill them for their home! Scarlets are a little less aggressive. Have you thought about Zebra Hermits?? The are usaully pretty cheap as well and seem to stay smaller then the scarlets. They are always roaming around especially when you put food in the tank they start crawling as fast as they can to get to the food!
Thanks, The reason why I like advice is because at ***** I bought what they called scarlet but after a month or so they were huge and they started eating my corals. I took them out and brought one to a good LFS and he told me they sold me reg. hermit crabs that are not reef safe!
Another vote for scarlets. Just a note: red legs are not the same as scarlets. I haven't looked at red legs, but scarlets have red legs/body and yellow eyestalks, dont get them confused. HTH.