Restoration druid is super fun and super good hands down! You can play it with 4/5 T9 for Reju crits, so in lower gear it is still healing a lot then switch to 4/5 T10 for more stats and decent set bonuses but not as good as the T9 set bonus. Resto druid can always be a part in the...
Feral tank druid is a good enough tank in this expansion, but with the Icecrown Citadel debuff (Chill of the Throne) you get -20% dodge which is the only avoidance for druids, but you have a lot of health. As a feral druid you have your own raid supports which is useful, druid is probably the 3rd tank after death...
Balance druid is a really useful spec to bring to any raids 10 or 25 alike. You have a lot of supports for the raid which I will list below and a good aoe burst and relatively good dps on bosses. Your dps relies on some RNG to have your Eclipse, without that buff on you you do way...
Feral dps really shines in ICC with the armor penetration cap achieved. Ferals is a good dps with a lot of supports that they can provide for the raid such as Innervate, Rebirth, 5% melee crit and so on. For guilds that are progressing with lower gear in a fresh ICC content it is advised to bring as much druids...