You would always base the ranking groups around a geared Warrior. You would run 1-2 in a WSG groups and up to 3 in AB groups. Most common was 1 for WSG and 2 for AB. However you often ran 2 or more Mages as well.
A pretty standard WSG group for Alliance would look like this:
Guarding flag room responsibility: 2 Players, Double Rogue or Rogue/Hunter. Mostly prevent people sneaking the flag out.
Ramp/Tunnel group, geared Warrior with double healers. Warrior always get Zerk Buff, unless you need to oneshot the other flag carrier, then a Mage picks it up, but the Mage could normally just take the other teams Zerk buff unless the other team was a premade as well. This is the main killing team, pretty much just killed anything moving in the middle of the map.
Raiding group: Have 1 druid, 1 healer(Normally Pala for BoF) and 3 DPS(Stack CC) to go get the other teams flag and get it to midfield using CC and escape. Where you get back up from the two other healers and the killing Warrior.
Repeat for easy 3-0 to your team.
A standard AB Alliance group would look something like this:
Stable Bitch: Hunter or Rogue, just to keep people from Ninjaing Stable. Normally only bitched about missing the action 8/10 games. Got really happy the few times they got 1-2 kills in a game.
Mines Rusher: Normally 2 players, often Mages due to slowfall combined with Arcane spec being the premium choice for raining death from above. They bumrush it, kill 2-3 players cap it. Leave one for bitch duty, the other runs off to join blacksmith in the middle.
Main groups based around Warriors with healers. Equally spread with 1 Warrior in each group. One Group goes Lumbermill, one goes middle. Crush majority of enemy resistance swiftly and then link up for pushing Farm and eventually into the spawn graveyard for an easy 3-6 minute game.
Warriors where also one of the main reason Mages saw so much play. You couldn't out DPS them, so you had to outburst the healers from range. And Mages could burst anything. It's amazing how Mages have been so good for every periode of WoW.