AIS does things that radar doesn't, and radar does things that AIS doesn't. Given a choice, I would take both. If forced to pick between the two, radar, hands down.
Radar works on all targets, not just those transmitting AIS.
Radar can triangulate off identifiable object to figure out your position, if necessary. Can't do that with AIS.
Radar will give you bearing, distance, and lat/lon of anything you point to. AIS can't do that.
Radar can track the movement of anything it sees, plot your crossing, and show you how to maneuver for a safer crossing. AIS can only do that for vessels transmitting AIS.
The only thing AIS can do that radar can't is tell you the name/call sign of an AIS target. In all other ways, radar is a superset of AIS. There is just no comparison.