Because I'm lazy, and because I (ahem) don't remember which comes first, you'll get a two-for-one deal on the loot that drops from the Coliseum this week.
And yes, I'll be lumping this in together in one big guide you'll be able to use.
I get a lot of questions about what you should upgrade, how you should upgrade it, where you should spend your badges first, etc. This...isn't really answerable for everyone, everywhere, but in general I agree with Jacemora in spirit. You should try and spend your emblems wisely on things that you won't quickly upgrade.
That means for bear, buy the tanking ring. For cat, buy the DPS ring. If you get a Trophy of the Crusade, get either the chest or the gloves depending on which will be a bigger upgrade for you, and gem it so you can use it for either set. Then work on the head and shoulder pieces.
The 4-piece bonus isn't worth it for either spec, honestly. It's good for cats, but it's nothing so insane that you must have it. The tier bonuses for bears are trivial. However, thanks to blizzard laziness, all the tier and non-tier gear have almost precisely the same base stats - which make them very interchangeable.
The long and short of that means that it will always - always - be a DPS upgrade to go up a tier regardless of what the piece is. This only applies to the coliseum gear, but it means that if you get an coliseum-10 piece, a coliseum-25 (or heroic 10)piece in the same slot will be an upgrade to it. And a heroic-25 will beat that. Always. That makes it a lot easier to evaluate gear.
The question then becomes - what should you really go for?
The big ticket item is the weapon. That remains the thing that's hardest to get and the biggest overall gain. Now, it's rumored that Onyxia drops an actual tanking polearm; if so, awesome for bears. Otherwise, it's the same as usual - look for the Lupine Longstaff/Twin Pact and grab it.
The other thing that makes recommendations difficult is that it's not clear how hard the hard modes actually are. Will the 10-man be fairly easy for 25-man raiders again? Will the 25-man hard modes be akin to Mimiron and Yogg, or Flame Leviathan? No one knows. My bet is that the hard modes will not be too difficult and most guilds will have all the hard modes done, and a few of them (like beasts and jaraxxus) will be done fairly early. That means lots of tier pieces, lots of high-end loot, and lots of good times. That's just a guess, though; we'll know more in 3 weeks.
Me personally? The biggest bang for the buck is the DPS ring for me, followed by the DPS idol. Then I'll go for the shoulders. Assuming I can do all 25, 10 and every daily heroic, that'll take me 3 more weeks to compile, and should put me in a good position to do hard mode content assuming no other upgrades.
Anyway, on to the gear lists.
25-man Faction Champions:
Satrina's Impending Scarab/Juggernaut's Vitality -drops from 25-man Faction Champions. (awesome for bear). This is a huge chunk of stamina that also adds...more health on emergency. It's a giant stam sandwich with extra stam. Now, keep in mind that you can't use this and the heroic version at the same time. However, also keep in mind that tanks are dirty bastards, and they'll fight you for this tooth and nail. Just get it and be happy, and pray it drops often so anyone who does tank can get it.
Ring of Callous Aggression/Band of Callous Aggression - drops from 25-man Faction Champions. #5 cat. This is a solid ring that isn't quite as good as dexterous brightstone ring, but is still likely an upgrade unless you've been very lucky with Algalon loot. I'd probably pass and get the badge ring first, but note that rings are sparse and competition is high; if you have the option, grabbing it isn't the worst thing you can do.
Treads of the Icewalker/Icewalker Treads - drops from 25-man Faction Champions. (#2 cat, #3 bear). These are about a 5-point upgrade from Runed Ironhide for bears and a 5 point for cats. Shockingly for bears, the thing that beats them? PvP gear. Still quite good, and because they're boots they can happily pull double duty for cat and bear. I'd definitely prioritize these if possible.
10-man Faction Champions:
Gloves of the Silver Assassin/Sunreaver Assassin Gloves - drops from 10-man Faction Champions. (#3 cat, #10 bear) - thanks to their poor stamina, these are worse than T8 gloves; skip if you're a bear. If you're a cat and you're not dealing with set bonus breaking, this can be a fairly strong choice; despite the item level they're just barely worse than the T9.25 pieces. As above I'd still likely pick the T9.25 piece and plan on using it for bear and cat, but this is a good stopgap, and if you don't already have T8 this is a very solid piece with tons of armor pen.
Victor's Call/Vengeance of the Forsaken - drops from 10-man Faction Champion. (?? cat, bleh bear) - this one is likely a big pass. It gives expertise, which isn't that special for cats, and it gives 1250 AP for a short time, which also isn't that special for cats. I'd ignore it unless your trinkets are atrocious or you're one of those freaks who doesn't like primal precision.
Fervor of the Frostborn/Eitrigg's Oath - drops from 10-man Faction Champions. (Bleh for cat, ?? for bears) - it's an interesting situational trinket that adds armor when you want it to (instead of The Black Heart) as well as adding about 2% dodge. That's okay (and stellar for Algalon) but fairly situational. Definitely grab it if it drops, but don't fight too hard if another tank wants it.
25-man Twin Valkyrs:
Lupine Longstaff/Twin's Pact - drops from 25-man Twin Valkyrs. (#5 bear, #4 cat) A really solid piece with good stamina and agility combined with the best threat stats for bear and the best DPS stats for cats. Only the weapon from Anub'Arak beats it in normal modes for cats, and only barely - we're talking a tenth of a point, if that. The Vezax hardmode staff (along with the pvp weapons) beat it for bears. If it drops, get it. It's really that simple. Don't wait for the slightly better piece. Just get it and be happy, and then get it again on hard mode.
Belt of the Merciless Killer/Belt of the Pitiless Killer - drops from 25-man Twin Valkyrs(#3 bear, #2 cat) This only loses to pvp gear for bears (along with the hard-mode upgrade), and this only loses to the hard mode upgrade for cats. Do keep in mind that for cats, you'll likely start wanting to bleed off hit, in which case something like the Soul-Devouring Cinch or Relic Hunter's Cord will start looking pretty tasty. And if you have the Soul, don't bother on this; it's barely an upgrade and may have more annoying itemization depending on what you have. It's also not a big upgrade no matter how you go; if you can get the Death-Warmed Belt made, do that first and only get this if no one else wants it.
Arbiter's Muse/Legionnaire's Gorget - drops from 25-man Twin Valkyrs (#2 bear, bleh for cats) - the only thing that beats this is the hard mode version. It's absolutely stellar for a bear, and beats the next option by about 10 rating points. I'd definitely try and get this if at all possible.
Death's Verdict/Death's Choice - drops from 25-man Twin Valkyrs (#2 cat, bleh for bears) - the hard mode version of this trinket is better, of course - but that doesn't mean this isn't amazing. It's not as good as a switch hitter trinket like DM:G is for bears, but 450 agility on a proc + 256 AP is a very, very strong trinket. Rawr has this version ranked 40 points higher than Mjolnir, if that tells you anything. It's a trinket, it'll have tons of competition, and you'll never see it again in your lifetime. Try and get it quickly if possible.
10-man Twin Valkyrs:
Armor of Shifting Shadows/Vest of Shifting Shadows - drops from 10-man Twin Valkyrs (#6 for cat, #7 for bears) This is an okay piece. It's only marginally better than the normal 25-man Hodir drop Winter's Icy Embrace for cats, and not as good as Embrace of the Gladiator. If you've been unlucky or want a marginal upgrade, grab it - but likely let others get it first. For bears, it's barely an upgrade over the Conqueror chest. I wouldn't bother at all with it there.
Loop of the Twin Valkyr/Band of the Twin Valkyr - drops from 10-man Twin Valkyrs( #5 bear, bleh for cats) - another high armor ring with good stamina and no parry? Sign me up! It's worse than the hard mode version, the hard mode agility ring mentioned above, and the Clutch of awesome. But that's it. And there's really not a lot of rings for bears, especially ones with armor. I'd definitely try for this if possible.