This thread is full of mis-directions.
If you want to do DPS (Damage) you can go either class. Both Vanguard AND Commando can do great DPS.
If you prefer to Tank, go Vanguard. All geared up and spec'd correctly it can be a good tank.
If you prefer to Heal, go Commando. Although that healing class is getting nerfed in the coming update, I'm not sure how great the healing will be after that. But if you like to heal that would be the class for you.
I have a level 50 vanguard spec'd for DPS and I love it.