Definitly go o-ring. I've been running Primary Drive stuff from Rockymountainatv. Cheap, and seems to work well.
However, after running into someone that was using Ironman sprockets I am sold, I will be dropping the cash on those next. He said he changes the chain every 130 hours, and was on the 3rd chain. His sprocket looked like new, even with over 260 hours of 510cc's worth of abuse by a AA desert scramble rider. I figure I'm getting about 40 hours our of my stuff, then it all needs replacing. He was running an hour meter, I am just guesstimating my time.