What do you intend to keep in the tank? Different corals and inhabitants require different flows. For soft corals a flow of maybe 10-20x the display volume is sufficient. For SPS or hard stony corals flows of 30-50x the display volume are not uncommon.
A good place to start could be as simple as a couple Koralia Evolutions 750 or 1050's and later add a timer or controller to switch them back and forth for more random flows.
Another, more expensive but very popular choice are the MP series powerheads which are controllable by themselves.
