Doesn't necessarily have to be the biggest win, but the one that you hold as your proudest victory.
For me, it is probably one of Chelsea 6-1 Tottenham, Chelsea 5-0 United (if I was going for big wins). 2 games where we played absolutely brilliant and crushed decent opponents.
I also hold the 0-3 win at OT as a proud victory too, same with the 1-4 at Anfield.
But for me personally, it would probably be the 97 Cup final win over Boro. There's always something special about winning the Cup, and we made a fantastic start and never looked back (sorry coop!)
If I was older, I would probably hold the Cup Winners Cup win over Real Madrid and the '71 FA Cup final win over Leeds (Osgood was supposedly fantastic in both matches) very high too.