So , I'll grant, that my experience with wow in general is kinda limited, but I've been playing tcgs for about 7 years. Every game tended to have a certain resource/non-resouce set up (magic/pokemon). Games that didn't heavily relied on more of a general or curve appeal to playing their cards (Lotr/Vs.System), since resouces with which to play cards were almost always there and no problem to play.

With wow we seem to get a little bit of both worlds. On one hand its recommended to play quests since they are, for the most part, optional.
Much like the game, sure you could just grind your avatar to the higher levels, but questing makes it so much easier. So far I've only played the demo decks and a few draft games over OCTGN/magic workstation/whatever with my buds. From looking at most of the cards, a lot of abilities and quests overlap. So, considering that in deck construction it really starts to open up.

Now lets look to abilities, if you haven't noticed there are quite a few general ablities, as well as the class specific ones, that overlap (with other abilities and quests). So you aren't a priest, but have an annoying abilties to deal with? Heres Burn Away. Want a blanket ally atk boost, but lack a warrior? How 'bout Rally the Troops or if you're on the kalimdor side of the world For the Horde! ?
Basically it comes down to that no one class doesn't have an answer in some way.

Allies have been kinda discussed quite a bit and they are definately dependant on what class you are running. Mages / Priests want protectors to set up their game, while hunters and warriors could benefit from just about any combative-type of ally. Pallys/Shamans/Druids like the game can fill multiple roles, so it all depends on how you roll. Rogues I think are either very ally dependant or not at all.That depeneds on the next area:

Equipment.

Sure we all know that the Horde warrior (who i can't remember at this point) is gonna be packing something big to smack you around with, but who is gonna bring some steel courage to the party? Well probably not mages and preists, they'll definately only have equipment to complement or improve their abilies, or rather, spells (Chromatic cloak, Whitemanes Chapeau). Druid are probably my favorite for this particular area, since they are the only class to have any decent power outside of weapons, Bear Form, FTW. Warriors will most likely be packing the most hard hitting equipment in the game. Shamans and Paladins can go just about any place with equipment. Pallys can be about as hard hitting as warriors, but as docile and supportive as a priest. Shamys are similar but are more akin to mages on the supportive side. Ah rogues, like their allies they can play with them or without them, but I see rogue decks as definately focused on one or the other.

So how does it all tie into a general deck composition idea, well I have one idea towards it:
10-20 Allies
10-20 Abilities
10-15 Quests
0-10 Equipment.

Granted this is just a light outline of an idea. Really there are no concrete deck composition numbers. It all depends on how you think a deck could be made out. In theory A mage deck could run a whole gamut of equipment and still be succesful, it just depends on how they run them.
Warriors could run no equipment whatsoever and still run you over with allies powered up by Battle shouts. Much like the game, theres a whole wide world out there and you have to explore it, but do it whichever way you like .

edit: most of the cards I put in didnt show up

the super math that people have been doing in the deck ratio thread (don't know if you've seen it yet) has come up with a minimum of 16 quest if you want a smooth number of them to show up. Most of those should carry some kind of draw (unless your picking up a lot of draw elsewhere like a pally or druid does.)

The rest does change from deck to deck.

It's also fun to see that without being outright 'stall' decks, games will fluctuate in how long they take depending on the type of opponents going at it. My friend and I used his new cards to do a pally vs priest fight, and we went on till like 12th turn because each of us had protection and healing.

I would agree with 16 as a min for Quests, and the rest depends on your strategy. If there was a class that could run with low ally numbers, it would be rogue, perhaps hunter. I would figure warrior to run the most allies...but I am generalizing and have not studied the entire set fully.

Coming from personal experience, although there hasn't been that much of that as of yet, I believe that running more Quests are vital to your deck. They help utilize EVERY card you put in your deck. Running anywhere from 16-20 is the best way to go, so you can be sure to always have a resource that is still going to be helpful later in the game. In addition, most of the quests out at the moment are there for card advantage, therefore thinning out your deck, and you will have made the most of your resources.
Just my two cents, Emphasis on MY - So I would't go by it...

now my experience has been limited to mages for the most part but i do agree with the suggestions of 15 or more quest , in my original play testing i was running 10 or less and that resulted in important instants and allies, and abilities in the resource row where they do me no good.

Quest counts are somewhat dependent on deck type. Decks focussed on curving out will play less quests than the reactive decks. Aggro decks want to maximise their early drops to make sure they hit them in the opening draw. The aggro mentality concedes that it won't win an attrition war, they are geared towards dropping men and swinging while the opponent is farting around setting up their engine.

On the other hand, control decks want to play quest after quest from their hand, dividing their resources between completing them and fending off the opponent until they can go for the win. I think that when the tournament level decks start to mature they'll run as few as 14 quests and as many as 21.

Ally counts will be similar to creature counts in M:tG. Some decks will play ~25, others will play 0. I'm not sure that there are decks that should play zero given the current cardpool, but I'd be happy to be shown wrong.
As for equipment, given the versatility of the equipment cards so far some decks will play them as freely as others play allies. It's conceivable that a deck could run any number up to about 20.

So 16 is a good minimum for quests, no matter the hero? I'm trying to throw together a Warrax deck, but so far I've only got 2 warrior abilities (both Rend).

In this game...there really is no specific deck composition.

Just as a quick example:

Generally hunter decks run tons of allies, less equipment and less abilities. Paladin decks will run a lot more equipment and abilites than allies. Shaman decks will be more evenly distributed.

So...deck composition shouldn't be game based...but rather deck/character based.

The only thing that may be similar across the board for all decks is the quest count. So far...just off the decks I've seen online. Somewhere between 12 and 18 is acceptable...thus the general preference to 16 per deck.

But thus far...there is no "set in stone" deck ratio unlike other games.

In a rogue deck like Timmo, a higher ally count like 20-22 is fine because the offensive fits with the board control that rogues have

yeah deck build ratios depend completely on the hero/build goal, not on the game itself. warrior decks could be running 0-4 allies, hunter decks 20-30.