2012 would've been the ideal time to go after his Mania storyline with HBK/HHH ended, however we wouldn't have got his fantastic Mania 29 against Punk.
2014 would've been another good time after the streak ended, but we were cutting it close to his 25th anniversary in the company.
2015 would be my answer. He was nowhere near his prime anymore, but he put on two fun, entertaining matches with Brock and we got to see the B.O.D. tag team one last time for his 25th anniversary.
He was shot beyond that point although his tag match with Roman against Drew and Shane was fun as was his Graveyard Match with AJ at the 2020 WrestleMania, He had workers that could help him out, sell, and not make him put in as much work.