you want auto reverse, which means 6 heads,
Playing back pre-recorded tapes, 7" reels, you want a deck with 3-3/4 and 7-1/2 IPS speeds. 15 and 30 are for semi-pro, not pre-recorded, and often decks with 15 ips do not have 3-3/4.
7-1/2 IPS is preferred, sounds better, but sometimes you will still want a tape that you can only find in 3-3/4.
I love my Teacs, x1000r and x200r, their last pro-sumer decks.