It definitely depends on what plants you want to keep. For plants that aren't very light-demanding (java, crypt, anubias, water sprite, etc.), I'd recommend a double T5HO (~3W/gal). However if you plan on keeping some cabomba, pennywort, cress, swords, etc., I would get at least a 4-bulb T5HO(~6W/gal) and use CO2 if you want them to thrive.
