If I'm outside shooting portraits with flash, I'm in Av mode almost exclusively. This allows me to get an appropriate exposure for the background (by the auto shutter speed setting) AND control DoF with my selected f-stop; manual would work fine too, but outdoor portrait sessions tend to be fast moving, and I don't have time to constantly be watching the meter reading. Besides, in Av mode, I can easily drag the shutter with exposure compensation, if the camera selects a shutter speed that is too slow. So outdoor with flash is almost always: Av, ISO 200, high-speed sync on.
Inside shooting portraits/parties/groups with flash, I'm in M mode almost exclusively; Av mode doesn't work with flash indoors because it will try to force you to use an unacceptably slow shutter speed. For indoor portraits with flash, I use ISO 200 (increases my guide number AND extends the life of my batteries vs. ISO 100, while retaining excellent S/N...I'll go to higher ISO if I have REALLY bad light or the subject is very far away), 1/250 (max sync speed of my 1DmkII), then select an appropriate f-stop to control DoF (and flash exposure in the rare instances that I use manual flash). Only in VERY poorly lit indoor scenes do I drop shutter speed below 1/250; again, no sense making my flash work harder than it needs to. So indoor with flash is always: M, ISO 200.
For landscape and cityscape photos (i.e. no flash), I'm Av, lowest possible ISO. Tv mode only when shutter speed and not DoF is the key determinant (i.e. handheld with no flash in a poorly-lit room, moving cars/bikes/trains/etc).