I think it would be nice to get daily challanges for the Game modes I am actually playing. Not everybody likes Versus, Escape, Horde. So why don’t let players choose which mode they want to have challenges for? Especially if you start to take hard Iron for it!
I suggested this same thing a while back. Different Tour of Duty challenges for every game mode. People can then grind out their ToD the way they most enjoy the game.