I replaced all my heads when i was able to afford it. I went to get evans
heads when the salesmen at guitar center told me to try aquarian
heads. I put performance II, two ply heads on the top, and classic clear gloss black single ply on the bottom. There was a big differance in sound quality. I put a hi-energy with a power dot on my snare, and a super kick double ply on my bass. I'm pretty happy with the aquarian
heads. You'll have to find what you like best.
I tighten my bottom heads a little tighter, but its personal prefrence, on the sound you want when tuning.