What Kind of Powerhead(s) are needed for a 40 Gallon Reef Tank [?]

I have a 40 gallon reef tank, it's just over a year old and my old powerhead has just given out on me. My question for all you Saltwater smarties out there is;



"what size of powerhead do I need for adequate water flow and is there a recommended brand to buy?"



And on a side note, is it better to have a lot of small to medium sized rocks or one or two larger rocks to have in a tank this size?



Thanks guys/gals