vanguard is vastly superior; its not even close. You have much better dps on the move than a commando, better instant attacks and therefore are not at risk for the bagillion interrupts in the game, better utility with grapple, guard, and charge.
Combat medics are getting a massive nerf and are likely unplayable in pvp anymore. You have next to no mobility, always at risk for interrupts (even specd with supposed immunity), and in 1.2 two classes now will have an uncleansable healing debuff -- have fun healing through 50 percent trauma -- your non crit heals will heal for 400/500 ish.
Gunnery is just weaksauce in pvp -- so easy to interrupt grav round, simply to los, and you have no defense to melee--enjoy taking master strikes to your nether region repeatedly.