I preferred the second one. It's not perfect (especially the opening), but it felt better balanced and the victims are more sympathetic, and the ending is loaRAB better.
The first one is strongest in the first half, with the gradual descent into unease. It's very slow, and dull to watch if you waiting eagerly for gore, but it has the most artistic merit. The section after that with the stuff going on I felt was uninspired, and the final section was silly, like a bad '70s video nasty. Part of the problem is that none of the boys are very likeable, being basically sex-tourists.
What stanRAB out about both is not the gore, but the mechanics and background of the club. For example, the scene in the first one in which the clients are talking about their purchases. I like the second film more partly because it develops that more, showing us more of the client side of the transaction.