Electronic properties of 2D MXenes can be tuned by their chemistry and structure. We report on THz conductivity and ultrafast photoexcited carrier dynamics in several members of MXene family with high intrinsic free carrier densities and carrier mobility. We find that MXenes of different chemistries respond to photoexcitation in dramatically different ways, exhibiting behaviors from conductivity suppression to long-lived photoconductivity. We discuss applications of MXenes in a variety of electro-optical and THz devices.