Hiya Steve,
I have tried many, I can't remember the name of the best one I found, we always used a common name (actually think it was the name my mum called it) but it was damned aggressive and when I tried one with discus, it went straight onto its side soooo..,. thats out.
Next best 've found is the Albino BN, don't know why but imo they are a tadge better than their duller brown cousins.
hth,