I don't know if anyone is reading this, but I've FINALLY settled on my Republic team composition:

Vanguard (Tank/DPS), Gunslinger (DPS), Commando (DPS/Healer), Sage (Healer)

I'm really hoping that the commandos get some kind of buff for their DPS by the time I get to 50. Right now, I'm thinking that the Grav Round armor debuff that they put on bosses is actually helping the overall team DPS to be higher. Combine that debuff with the ability to do backup healing and you've got a great utility character. The Gunslinger puts out some pretty awesome DPS.

I did Athiss with the above team when the gunslinger was 4 levels behind the Commando and in some situations my gunslinger was putting out more DPS than the Commando! For raw ranged DPS, there is no rival to the Gunslinger/Sniper.