The title itself says it all. What card that you've purchased, not pulled, have you gotten the most use out of?
For me it's easily been 94 OVR Harold Fannin (215k investment). I bought him for 200k when he was still in packs, added the TT for 15k, and he has been my TE for 3 months. Was easily the best receiving/blocking TE when he was released. I don't even run abilities on him currently, yet he still gets me plenty of goalline TDs with his impressive CIT. I can quick sell him for 175k and be out only 30k on a card that's gotten me 465 catches, 6792 yards, and 74 TDs in H2H alone.