I had to sort of lightly skim over what's been said as I haven't seen 6 yet and don't want any spoilers :p.
Saw 1 has to be my favorite.. its almost for the same reason as music artists. The first album they release really shows who they are and what they can do because they're giving it their all to try and make it big. That's the way I feel about Saw 1. However, I do like them all (save for 6 since I haven't seen it), and own unrated collector editions of them (and c'mon, its Saw, you HAVE to go unrated).
I suppose Saw 3 would be my second favorite. Followed by 4, then 5, then 2. Other than the idea of continuing the story I didn't really care that much for 2 and 5. They were just a little less believable and less compelling. For instance, in Saw 2 it seemed like I was watching two different movies until the end where strings finally started tying together. The same thing happened in Saw 5 except this time the "group" of victims were completely unrelated to the actual Saw story other than being a method to frame Strom.
Anyway.. I have noticed there's a Saw video game. Has anyone played it? I've looked at it a few times but I just keep thinking about whats happened in the past when games are made out of movies.