AlbinoCow
Vaco Del Blanco
Anyone arguing in favor of Protection Paladins or Guardian Druids apparently never played a premade and therefore doesn't have a clear idea about how a premade and its rules look like.
Protection Paladins are absolutely awful for premade FCing. They gain zero passive mitigation, they have no reliable mobility whatsoever, LoH doesn't require you to be the person carrying the flag and the CC they have in HoJ and AS doesn't make up for their more than lackluster kit. They also need to stand still to produce any kind of significant healing which is not acceptable for a flag carrier.
Guardian Druids have the highest mobility out of all tank specs, decent mitigation, some healing in Rejuvenation and roots. Their mitigation gets outclassed by warriors. Their healing is not significant enough to make a difference when under pressure. Your CC, again, doesn't require you to be the actual FC. The mobility can come in handy, however in a premade situation with a warrior FC you simply send your resto druid / boomkin to pick up the flag, once you are in mid with your team your mobility will be irrelevant. All the aforementioned perks require you to shift out of bear form, losing your mitigation entirely. Those reasons alone are already enough to pick a warrior over a druid, the biggest downside however is a part of the common premade rules: A maximum of two of one class. You gain nothing from using a druid FC that would justify dropping either a boomkin or a resto druid.
Protection Warriors have the highest mitigation in the bracket, they have some mobility in Charge and their other two specs are entirely useless for premade purposes. They can also be Goblins which is the best horde race for flag carriers. Warriors are by far your best choice.
Also, I saw someone complain about the implication that flag carriers would basically afk for almost the entire game, making their CC and mobility useless. That is exactly what FCs are supposed to do. They sit between thirty and fourty yards behind their healers to make it as hard as possible for the other team to swap to them, and to make them cover as much as ground possible when trying to push in. When that happens the only role your flag carrier has is to absorb as much damage as possible, LoS if available and watch his healers position.
In most cases they don't even pick the flags up themselves, they can't if the opposing team is not pushed back into their own graveyard and has atleast one decent hunter. They will usually have a druid bring them the flag, as mentioned before.
TL;DR: A flag carrier's job is to be able to take a beating, Protection Warrior does it best with the least downsides.
Im pretty sure the role of a fc is to not take a beating. If u win a game and ur fc is untouched, that's a good thing isn't it? You could send a druid to go get the flag, but then ur mid team will be weaker. Rather than sacrificing a boomkin or resto druid, you can keep all ur dps and healers in mid while a guardian druid grabs the flag. I must agree that running a guardian druid can restrict ur comp, but I believe wild charging above gy, and other possibilities in ramp to roof area, more than makes up for it. Also while getting caught out of bear form is a noobish thing to do in a premade, u still maintain the same amount of spell dmg mitigation, and ur physical dmg mitigation is roughly the same as a hpally. Wild charge can be used to mitigate an un-definite amount of dmg and even take u from being in the worst position as a fc, to the best one