Since you posted in the commuting forum, I assume you want answers for commuting. 29s just don't work as well, particularly if you need to start/stop and accelerate frequently, have to deal with sharp turns and quick moves, and want something that's very responsive. However 29s are fine if your commute involves just a long raod/path without much stopping.

I use a 26 hardtail for commuting but wouldn't want to use a 29 for the same route