It all does about the same thing. The biggest difference I know of is the new ester forms of creatine don't take as long to load into your system and are less likely to cause stomach problems. I like BSN products myself but as I said before, it all works about the same.
I used to use monohydrate, but the bloating and upset stomach are no fun. I've since switched to the new "buffered creatine" and I absolutely love it. No bloating or gastro problems. Great pumps. And CHEAP compared to the other. No loading phase. Its the Kre Alkalyn stuff. Two pills a day. Its by far a better product.
I'd start with the cheapest monohydrate. If it works and doensn't cause sides, stick with it. It works for me, others get stomach and other digestion issues. If that happens try the more expensive stuff.