A. ocellaris
In which case I would suggest a BTA, considering they are a bit less difficult to care for than other anemones. They will wander, but once they find a nice spot they will stay there for a long time.
BTAs will attach themselves to rock, so I would suggest building a rock pile in the tank. They can get about 24" across, but they also split, which you could always trade off. IME, BTAs like moderate flow. Make sure you cover powehead intakes, because these guys can get quite adventurous.