Hmm, let see, that is quite a difficult question in general. If it were about DVDrips, I would definitely go for ViSiON. But for BD/BDRips, my choice is always FLAWL3SS. I have seen some amazing stuff from them (for the size given) in the past, so when I have to choose between both groups, I always pick FLAWL3SS, if possible. Maybe it is rather psychological, but then I know I won´t regret downloading it (that is, if I really have to pick BD/BR) and I know for sure that they always deliver what is expected - a good BD/BRrip, no more, no less
Having said this, I have seen better BR/BD from "independent" encoders. But these are kind of random, so, unless you know the guy´s encoding history pretty well, you basically never know what you are downloading and how good it would be compared to the well-known groups. Truth is there is often too much crap... But then again you might just get lucky.
There is also this group Kickass torrents or something. They seem to deliver BD/BR quality within some amzing file sizes (like 500-800 MB for full-lenght movies), but quality is not constant and can´t be expected to be so, given their encoding priorities.