I have used the following for patrol: G2x Tactical, G2x Pro, and Streamlight Pro Tac HL. Started with the Tactical. It is a great light, but it kind of sucks only having the full power mode. You easily blind yourself when using it for simple tasks (reading, looking for something in the patrol car, etc). It then got moved to my patrol rifle in an IWC mount... perfect light for that role.
Then went to the Pro. It has the same max output but also has the usable low light setting. The only problem with that is you have to hit the button twice to hit the high setting. Not great for a patrol light IMO. High stress situation at night I don't want to have to cycle to a high power setting. This is now my backup light and stays in my patrol bag.
Finally tried the Pro Tac HL and have been extremely happy. Everyone on my shift has since bought one to compliment the TLR-1 HL's we are issued for our handguns. It is very bright (600 lumens?) on the first press, second tap is strobe which I have found very useful for directing traffic/ crash scenes, and the last setting is low which is also very useful. I haven't really played with the programmable settings but I know you can remove the last two options and have just max power. I carry this light on my duty belt in one of the molded plastic surefire holsters.
I believe all three cost about the same, $70. If you don't mind only having one light output then the G2x will definitely stand up to patrol both on your belt and on your gun.