I think ebo-jager are the uber badazz heaters. Visitherm aren't bad either. I would definitely stay away from the real cheap stuff you can find over at petsmart...
I use a single 250w Ebo-Jager in my 125g african tank and it handles the load just fine. Redundancy is a good thing, so if you can afford two I'd do it. Ebo's are expensive little toys though.