A tie between Far Cry 3, Far Cry 4, and Watch Dogs.
Actually, I never preordered Far Cry 3, but I did buy it launch day, so I guess that sort of counts.
The thing was, none of them were bad games, they just had shitty optimization. Every single one of them had stuttering issues and horrible texture issues that I had to wait over a month for them to be patched.
Far Cry 3 did eventually become fully playable for me, AFTER an expensive system upgrade, and AFTER several patches spread out over a month and a half.
Watch Dogs also became playable, but only with settings like Object detail and shadow resolution being turned down, along with several patches.
And I'm still waiting on Far Cry 4. Stutters almost worse than Far Cry 3 did in most cases. I mean, yes, these games are rather pretty, but 16GB of RAM, an overclocked AMD 8350, and a factory overclocked 780ti shouldn't be lagging.
*sigh*...I guess I'll just have to learn my lesson and not preorder or even buy anything Ubisoft is remotely behind. Though The Crew is surprisingly polished so far. No stuttering, decent visuals, and great optimization on my end. Too bad it's a mediocre racing game at best so far.