I'm new at this too but from what I've read larger output powerheads seem to be the order of the day.
I have a new 46gal tank with a canister and a HOB
filter. I have 2 power heads (AC301 & 401). The 301 is mounted midway down the glass and discharges directly across the back glass and behind the live rock to avoid any stagnation problems in this narrow area. The larger power head is mounted high and discharges diagonally across the center of the tank.
The two filters discharge in two other directions.
If someone has a comment on my PH set-up I'd be interestied in hearing it. Like I said; I'm new to all of this too.