I just did a test with the explosive perk on a tank with each launcher.
About 60m away per hit:
RPG - 43pts
CG - 28pts
AT - 36pts
It took the RPG and AT three shots to kill the tank while the CG took four.
I already Plat the CG long ago so I will switch over to RPG just to blow up vehicles.
The irony is that the CG is better for Heli kills and infantry. The RPG is great for all vehicle kills.
http://denkirson.xanga.com/722757523/bad-company-2/
No need for testing
CG has larger splash damage and is a 1 shot kill for infantry w/o body armor (which is why I run body armor).
Heli will go down in 1 shot with either the CG or the RPG, it's just infinitely easier to hit a heli w/o a tracer with the CG.
I have ~1300 kills with the RPG. It's best used with tracers against tanks/heli's though it does kill everything. It's a bit harder to use than the CG, but not much different. Much harder to hit things that are far away.