hman–Well, first of all, realize that pretty much any giant croc/’gator movie is going to suck hard. It’s then a matter of whether it’s fun bad or just plain bad. (Except, as noted above, Rogue, which I definitely recommend.)
Blood Surf–It’s quite bad, but it leans more towards fun bad I think. I thought it was pretty fun.
Croc–takes a while to get going, but ends up fairly decent. (Michael Madsen’s in it, so that’s a bonus.) Crocodile is crap. Utter crap. So is the second one, although it occasionally wanders into hilariously bad territory (be prepared for a lot of “cool” cursing though. My late grandfather swore less, and he was in the Navy.)
Dinocroc‘s beastie isn’t a traditional croc, but it’s probably the most fun film listed here. Keep in mind that it’s still bad, just entertainingly so.

Haven’t heard much good about Primeval or Lake Placid 2 (which makes sense since the first one sucks), and even less about Supergator.

Matthew, I think I can say without fear of contradiction that this is rather better than either of Tobe’s efforts. Which statement just might take “damning with faint praise” to new heights.