I've played at Chilli Paintball pits, which was really sweet, Action Park in Joliet, which was ok except we had to sit around more than we played, Pekin, which was ok, Area 52 in Mackinaw, which is too small and boring, and that's about it.
I think that Sudden Impact is the best field I have ever played at. Some of the other reviews say how the fields aren't that great, but they must have changed since the last time they went, because they now have an airball field and a hyper ball field as well as a speedball field. I think the woods fields are great too, because it's a lot of natural cover mixed with spools and the like. The refs are all really great, and the owner John is a nice guy. They do a good job spliiting up the different levels of players, unlike most fields. The field is also very safe. When I went to the Area 52 in Mackinaw, people were walkin around w/ their barrel plugs out, shooting in the staging area, and none of the refs cared. At Sudden Impact, they make sure that everyone's safe and they do a good job letting everyone have fun at the same time. They also have been having a Big Game the past few years which is a lot of fun, and they host quite a few big tournaments as well. All in all it is a great field that I have been playing at almost every Saturday for the past 3 years and I encourage everyone to go there and play.