If you're just getting fish then the light doesn't really matter. You don't need anything particularly bright; a high colour temperature is what will really make them pop (I use a standard 20W T8 fluorescent in 18,000K on my 37gal FOWLR
and the fish look great).
If you're doing corals, then you should probably have an idea of what corals you want before you set up the tank so you can set everything up to maximize those specific corals' needs. Specifically, you'll have to do research on those corals' light requirements and choose a light accordingly.