Because that's a very subjective answer. I've had a lot of issues with ComEmu. On several occasions, (I'm speculating that it's been after updates) it seems to completely forget all of my settings, and revert to defaults. It happened several times when I didn't have the time to track down the problem, so I've stopped using it.
Cmder is just a shortcut to using ConEmu. It literally is ConEmu with a different set of default settings and some extras preinstalled.
Never happened to me. However, it seems to mess up ncurses rendering (eg, tig is broken on my work laptop).