Creatine is the tried and true. There are many studies on its efficacy, and it is quite cheap.
CEE is newer, and there are no studies showing that it is better than mono. And its a bit more expensive.
On the other hand, user reports on CEE are terrible. People who don't respond to mono are using CEE to great effect. You need less CEE for the same results, and it doesn't cause the gastric upset and bloating that many report from mono.