healer or mdps for low fps?

I get low fps in 25 fights,about 15-20 fps,which class to choose for low fps? (wotlk wise)

*i'd like to play RestoDruid or FuryWarrior,which one fills its role better with low fps?

Thanks,

Generally I would not suggest you to roll healer, since many raid encounters heavily depends on healer skills, but if you want healer anyways resto druid and disc priests are the best choice because they can work pro-actively - pre-shield, pre-hot. Re-active healer spec with low fps will get raid killed. Holy pala also can work in raids where you need to heal only tank. Resto shaman mainly spam chain heal, but they should also give fast greater healing waves to top off low health targets, with low fps it can be deadly.
Fury warrior is also good choice if you have low fps, since their main dps skills have cooldowns and you dont have to spend for example energy and runes as fast as you can. I would avoid casters, even dot classes. Ret, warrior, hunter is good choice.

Tank or dps. (I'm playing Ret/Prot)
I'm doing 25n/hc raids on 10-15 fps and I don't have problems with dying because of it (except on Anub in toc25hc when being OT - really hard to get adds sometimes, and LK on HC can be really tough at moments). Marogwar is also a bit tricky as mdps but once you get used to that fps it'll be np (as far as I did 25hc, I don't remember dying at all in flames).
But then again, on Marogwar/LK/Anub my fps goes as far as 3-5 fps, and I really hope that minimum you can get is 15. :D
As healer I had really hard time in any of the big raids, so I would recommend avoiding being healer.

I don't know your settings, but if you didn't already, when in raid turn everything off/on lowest, except view distance (this one is useless in most raids and doesn't improve fps - sometimes makes it even worse)