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).
Pretty much the same deal. BBTV was cagey, promised the moon, but did not want to put things on paper, whereas S71 went the extra mile to prove they are legit so I went with them. S71 deal not quite as good as BBTV's, but I felt like S71 only signs people they want whereas BBTV just wants to fill their coffers with as many channels as possible.
Hopefully it goes well.
Only thing that concerns me is that a lot of the competitor channels are with BBTV, and it seems like they are pretty skilled in the dark arts of tags, title, click bait thumbnails, etc., whereas S71 you don't see as often, but when you do, the channel is huge. I guess time will tell, I hope both networks are equally skilled.