Tru feeds. They typically hold 13 paintballs as well (12 fsr). I have both and I much prefer the trufeeds over the Zeta's. as you have to release the spring manually with Zetas and balls fall out of the bottom of Zetas if you don't use the cap (and no one does as they are a pain in the butt...).
Plus they drop out the mags when you have them in your drop sac as well. The trufeeds are beefier and don't have as many breaking issues as they are made much stronger.
Plus they have a handle so you know without looking that you have the right side and are trying to insert it the correct direction. Makes loading without looking easier.