It also depends on what type of inhabitants you want to keep. One time I had a Red Sea Max and I kept it cold (72-73) so I could have Catalina Gobies and Blue Spot Jawfish. The bluespots don't HAVE to have cold water but I think they prefer it. Catalinas on the other hand are something you REALLY should not keep in a warmer tank.
I know, I know...everyone says "but I've got one at 80F and it's FINE." Well, how long was it fine? Not long, I would guess. Anyway, so I kept the tank cold and had those guys and it was awesome.
I think my current tank is 77 degrees or so but I just put up the MH yesterday so we'll see what the temp gets up to. I may have to crank the heater a bit more to avoid a swing in temp.