My first is a combo of six games in chronological order, all for Nintendo 64:
WCW vs. NWO: World Tour(1997)
Virtual Pro Wrestling(1997)
WCW vs. NWO: Revenge(1998)
WWF Wrestlemania 2000(1999)
Virtual Pro Wrestling 2(1999)
WWF No Mercy(2000)
Each game is a wrestling game developed by AKI. They are, to me, the pinnacle of wrestling games. I played each until the next one came out. Overall, I can honestly say I locked in a good 1,000 hours on those games. I cannot seperate and name my favorite from them because they're all so different.
As a runner-up: Marvel vs. Capcom 2 for the Dreamcast.