I actually had to decide between these two as well (almost a year ago). Studio71 offered a lot of stuff, but when I insisted they put it all on the paper (in contract), they said they can't do that. I think that says a lot. They offered 90/10 rev share if I'm not mistaken, although it was lower at first, but even increased it was easily beaten by BBTV's deal (worth noting that I was with BBTV for a year before that).
Who do you like better? I've noticed Studio71 is more willing to put things on paper than BBTV, who seems to want to be take it or leave it.
I haven't been part of Studio71 so it's hard to tell. If you can get them to write down some of their promises and opportunities they told you about, it may not be a bad idea to just go for it! They did sound very professional at start of last year, I'm sure that didn't change for the worse.
BBTV is absolutely massive and they are definitely not going to dedicate as much time to you as S71 might. I'm curious though, what kind of a deal did BBTV offer you? Perhaps you could get it higher (of course, it depends on channel size).