What I'd recommend is really about what you're looking for, If you just want to grind with the bros to 80 you don't really even need a full-time dedicated tank. You only really need the full tank complement when you're doing raids or attempting dungeons at a lower level than you should.
XP is fast here, So you really won't spend -much- time leveling (40-60hrs)
Any plate class (and feral, even cat-spec druid) is going to be tanky enough to level to 80.
Threat against a hunter is a non-issue (they can MD threat to you and can just drop threat with feign death or use deterrance and be immune for a while)
If you want to tank for a living (after hitting 80) you'll see much more tank action as a Paladin/DK/Bear than a warrior
If you just want to be a tank for your 3man group, you don't even need to go for tank spec (plate armour is enough for leveling) and could just go with DPS gear as well.
If you want to bring the most bonuses to your 3man group, Paladin is definitely the choice, as they're bringing Buffs (+manaregen OR +AP OR +10% stats) Aura of choice (+armor/fire/cold /shadow resistance/crusader) for survivability
Crusader aura +mountspeed for the group is one of the best time-savers in the game, although you won't get crusader until 62
You already have a druid in the group, so you kind of miss out if you're also a druid, as you have almost identical buffs.
If you don't go paladin, you'll have no reliable way to dispel magic/diseases which sucks.
Really, What do you want to do at 80? Warriors and Paladin and Druids are all fun, but if you're going to have more fun tanking than DPSing, you definitely want to avoid warrior, as they're the least likely to tank of all the tank classes (again, they're not bad tanks, they're just shunned almost as bad as wf shamans are. On icecrown, at least)
If you want to bring the most to the 3man group, you probably want to avoid Druid or Warrior. Although as a druid, you can at least get 1 battle rez and a free mana boost to your healer (innervate).
If tanking past 80 isn't important to you, any of the platers are going to be able to tank in DPS gear/spec (War in dps spec, pal with righteous fury +threat) while leveling, especially with a dedicated healer backup.
As far as difficulty, ferals are probably the more complex choices for tanks/dps as far as basic ability usage goes, since they have to learn essentially 3x sets of abilities from the start (Spells, Catform skills, Bearform skills, I'd put them somewhere around DK difficulty), and they generally need to spec towards tank (bear) talents+glyphs or DPS (cat) talents+glyphs. many cat talents don't benefit bear and many bear talents don't benefit cat. A cat specced feral going bearform is going to lose most of their DPS, a bear specced feral going catform is going to do abysmal DPS. A warrior can just change stance and he's enough of a tank to hold aggro and still do decent damage in dps gear/talent, a ret paladin can just use RF and he'll have enough aggro and his damage output won't change. (They can't do this in raid situations but really should be fine while leveling)
If you're worried about difficulty because you're new, Definitely go Paladin. They have the least things to worry about, and bring the most bonuses to your friends.
Edit: Just realized you mentioned all 3 of you are beginners, If you do want to tank full-time, you could go the full faceroll route, and do 3 paladins (Prot[tank]/Holy[heals]/Ret[dps]) Probably not the best option (paladin population is already bloated) but they're all easy to get started with, you get all the paladin buffs, multiple aura buffs, and you wouldn't need to separate to do your class quests.