In my experience, i started initially with a Vanguard and Commando duo, got them both to 50 and then wanted to try 4 boxing. At this time im currently leveling a Guardian, Sage, Commando, and Shadow, for a completely mixed group, sitting at level 40 atm.

In terms of the tank aspect, i have not decided if i like the Guardian over the Vanguard at this time.

From the DPS aspect, like a few others have stated, Same class makes is so much more enjoyable. I also find that using Sentinel/Shadow for melee DPS can be a hassle sometimes especially in a mixed composition group. If you go all melee that would be different, but having 2 ranged(healer/ranged dps) and 2 melee(tank/melee) positioning and your keymaps get jacked up and confusing sometimes. I had to rebuild my Keymaps several times learning/trying/design/figuring out even with the input from this forum, and im in the process of planning entirely new keymaps out. As for my currently DPS setup Sage/Healer casting Distrubance when i can afford it, the Shadow DPS, and Gunnery Commando, i usually do not have issues taking on Champions , however i find that some of the champions that have aoe abilities, moving around melee with the current style of follow we have can be a headache sometimes. After this team is 50 i will most likely level 2 more gunnery commandos or 2 more Tele/Balance Sages.

As for the healer, i personally have more experience on a Commando Healer raiding as it was my original main. Commandos are amazing single target healers, currently pre-1.2, commando healers have very very bad aoe healing and quick spot healing they do get an instant heal with a large cooldown, but that's not enough a lot of our current healing revolves around making sure we use another ability prior to enhance the ability of our next heal. In my opinion, and with some reviewing on the PTS, Post 1.2 they are nerfing some of our burst healing for PVP reasons and reducing some of the bonuses we get on healing pvp reasons, which affect the class overall; however even with the increase of 3 to 4 on the kolto bomb, it still will not make our aoe healing any better as the radius of it is so small.

I am currently preferring a Sage healer at this time pre-1.2. Post-1.2 im not sure as im not 50 with my sage yet. The over-all Force management and general abilities are much more direct and efficient when comparing it to a Commandos, not to mention their aoe heal has a larger radius and hits up to 8 people. Sages get force armor that shields for more and longer. Yes commandos get a sort-of-shield, but it requires you do Bacta-Infusion first before being able to shield someone using kolto-bomb.

So all in all, im having an enjoyable time, however i need to really streamline my macros within isboxer to make effort more manageable. Right now i having issues with getting overwhelmed with elite mobs 3 to 4 and i have an issue keeping them on my guardian and off my healer.