You can also consider hybrids if you're a player who can juggle both offense and defense and prioritize quickly and correctly. Their heals are as big as healer heals; just can't spam more than 5 in a row without going oom. Moonkin can get top dmg in EVERY battleground(above all the surv hunters, even 29s with pocket healers) while also off-healing team-mates pretty frequently. Sometimes, when the healers are bad, you get top healing too. But it's a different play-style.
The huge advantage is that blizzard now tries to match teams with even numbers of each role. So if one team has 2 healers the other team will most likely have 2. Playing a well-played hybrid lets you sneak in half a healer without taking up an actual healer slot, so your team has more total healing. If you're a moonkin, you don't really sacrifice dmg to do this, because most of your dmg is DoTs, and they keep ticking while you heal.
If you want to be a pure healer who doesn't have to dps in order to maximize his potential, try holy priest.
(Disc is better but it requires hybrid play style to maximize, i.e., keeping SWP dot on as many targets as possible while using schism into penance on cooldown while keeping atonement up on 2 friendly targets who are not already at full health, while also not letting anyone die(flash heal) - very tricky to maximize. Disc playstyle is that of a hybrid, like moonkin. It's stronger overall, but takes a healer slot from another disc. So you're only a net-gain for your team by being a better disc than the other ones.)
Holy is mostly just about healing people non-stop. Strong, and easier to be good at than Disc. However, you will occupy one of your team's healer slots instead of a possible disc, and will need to out-perform them to be a net-gain for the team. This is possible as holy, but you're at a slight disadvantage to disc.
I'd say you're better off just learing Disc or Moonkin.
Rshaman is a second tier healer. Not far behind. You can sort of hold your own, but I don't see a strong reason to play it in bgs.
MW can put out top heaing in an ideal situation, but that's not the most common situation, and they die easily. They can't counter burst. They counter DoTs, but not burst, and it's a burst-y bracket.
Rdruid is still last; the HoTs are small and weak, and people die too fast; the HoTs don't have time to tick. They can FC in pre-made games where they don't take up a healer slot, but make terrible FCs in random bgs, for the hidden reason that they rob the team of a healer. At 4 stacks, you lose all the druid mobility. The bear form is not nearly as good as having a healer (the one whose place you took) spamming heals on you. (They still make the best FCs in pre-mades.)
