Not really picky in this department. But, it will all depend on the size of the tank. Fluval E series work good in the smaller tank department, But, I dig Stealth in the bigger tank department.
I have a Rena inline 300w heater on my system. I love it. Looks good, works well, and heats the water evenly.
I just had a marineland 200w blow up on me. Sounded like a gunshot muffled underwater. Got another one because my LFS is awesome and they exchanged it.