Think of Tv and Av as a means of the camera setting one parameter, while you set the other. You select Aperture (Av) or you select Shutter Speed (Tv); and there is NO SINGLE 'best' for a given situation!
For example, if you are shooting a waterfall and want the smooth flowing look to the water, you might want to use 1/8 sec. and shoot with that on Tv mode and let the camera choose the aperture.
On the other hand, shooting the same waterfall, you might want deep DOF and so you select f/11 with the camera on Tv, and let the camera choose 1/100. See how each mode is useful for the waterfall?! No single answer, but one which is driven by what YOU as the photographer wish to achieve!