Just to add a few things (I've made the titles clickable links)...
Dengar (p2w)Basic = Assist chance. 1st Special = Speed Down chance (3 turn CD). 2nd Special = Tenacity Down chance, DoT chance & TM Down chance. Passive = TM Up chance on Enemy Dodge.
CT-7567 'Rex' (p2w)100% chance of 25% Turn Meter removal on Basic Attack (subject to tenacity/resistance/evasion, of course). Even Teebo has to be stealthed before he has 100% (although his is 100% TM).
ReyShe can cause a wipe, if you're not careful. Basically, Bosses (Captain & Rancor) gain 5% Turn Meter every time they take damage. Rey's second skill (Leverage) is fine to use and counts as a single hit. Her third skill (Flurry of Blows) however, is 2, 3 or even 4 hits. If the Boss has over half a bar of Turn Meter, don't use it unless you're confident that you're not going to trigger his next turn.
ST HanPeople seem to forget that he's not just there to taunt. His Turn Meter removal 'passive' (Bluff) is pretty handy. While taunting he will also give allies TM when damaged.
Ahsoka TanoI'd argue that you can add her to the list of 'Evasion' Leaders. She only synergises with Jedi & Nightsisters though.
Tusken RaiderI don't hear him mentioned much, but he has a decent damage TM reducing basic. He's not ideal for your A-Team, but I think he's good for further down the order. I feel that he might shine in the future, if more Tuskens are added.
HealersMostly agree that they have limited utility, except for a few who are actually reasonably good attackers (Luminara, Ahsoka, Chirpa, etc.).
Debuffers/CleansersI don't find them particularly useful. The link above may interest you regardless.
Finally...
People have solo'd the t7 (meaning they have started the raid from the beginning and completed it without anyone else's input) using the following teams (These characters would obviously also work in t1-6). Images are behind spoiler tags.
- Teebo (L), Dengar, QGJ, Rex & GS.
- Teebo (L), Dengar, QGJ, Fives & Rex.
- Teebo (L), Ewok Elder, QGJ, Fives & Rex.
So that should give you an idea who is regarded as key.
The best f2p team you can construct from that is...
- Teebo (L), Ewok Elder, QGJ, Fives & GS.
Which matches Wakson's recommendation exactly (go figure). lol
One more small thing... I don't mind RG. He just needs a good potency bump to make up for his shortfall and his auto-taunt has saved my run on more than one occasion too. Gotta admit that Fives seems a better alternative though.