About to buy some powerheads, and I would like some advice for a 55g.

[ScubaSteve]

Well, first question is: what live stock are you planning on keeping (in terms of corals)?

Tunze and Vortechs are on opposite ends of the spectrum in terms of flow philosophy: tunze creates, more or less, strong laminar flow that can reach the opposite side of the tank where Vortechs create a wide turbulent field. Personally, I prefer the Vortechs not only for the flow patterns but for the overall product design and low profile.