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

[gregzz4]

2 is better than 1
One left and one right

Cross-flow with one master and one slave
This will give you the back and forth flow your tank needs
If it wasn't a 55g long, I may say different, but your long tank needs the flow of 2 pumps, regardless of what you buy

If you get Vortechs, make sure you get ones that are wireless if you want the true Eco versions aka MP10wES is wireless and EcoSmart

This will give you the full abilities to create all kinds of flow patterns ... love these pumps

If this was a 55g cube, you could get away with one MP40