This question gets asked around a few times, Toughness or Anticipation? Some say get both, some can't get both in their spec though and have to choose.

What people want to choose is their own choice, i prefer Toughness (Thick Hide for druids though they don't have Anticipation or something similar :P).

Some people, however, have said that because of the Diminishing Returns on armor MITIGATION (not armor itself though), Toughness gets less effective the more armor you gain. I tended to disagree mostly since the more armor you gain, the more toughness grants you as well. There was no math on the subject however, so i decided to do it.

Formula used for armor:
mit(armor,level) = armor / (armor + 467.5 * level - 22168)

Formula used for "less damage taken" with 5/5 Toughness (aka. if the result is 5% a 100 hit will hit you for 95 if you gain 5/5 toughness):
100 - 100 * (1 - mit(armor * 1.1+1500,73)) / ( 1 - mit(armor+1500,73))

+1500 is the armor that is NOT affected by Toughness. This means Devotion Aura, Armor Pots and armor from agility. For this i assumed 1500 buff armor (Devotion Aura, MotW and agility, standard raid buffs with no pots).

Here is the math results.

9k base armor before Toughness (10.5k after buffs): 5/5 Toughness reduces all direct melee damage taken by 3.85%
10k base armor before Toughness (11.5k after buffs): 5/5 Toughness reduces all direct melee damage taken by 4.08%
11k base armor before Toughness (12.5k after buffs): 5/5 Toughness reduces all direct melee damage taken by 4.30%
12k base armor before Toughness (13.5k after buffs): 5/5 Toughness reduces all direct melee damage taken by 4.50%
13k base armor before Toughness (14.5k after buffs): 5/5 Toughness reduces all direct melee damage taken by 4.68%
14k base armor before Toughness (15.5k after buffs): 5/5 Toughness reduces all direct melee damage taken by 4.85%
15k base armor before Toughness (16.5k after buffs): 5/5 Toughness reduces all direct melee damage taken by 5.00%
16k base armor before Toughness (17.5k after buffs): 5/5 Toughness reduces all direct melee damage taken by 5.15%

As we can clearly see, the better your armor gear gets, the more value you gain from toughness. So in other words, it doesn't get less effective the more armor you get, it actually gets more effective. Same thing applies to other armor multipliers like Inspiration etc. which will mean that the tank with the most armor (druid) will gain a bit more benefit from those armor increasing procs, as long as he doesn't pass the armor cap of course.

I prefer Toughness as well, since it always is working for you no matter where you are getting hit in melee. I thought the designers hinted that because Toughness is at Tier 2 for Warriors.

You didn't how the mitigation of 20 defense though (to more clearly show why toughness is generally better).

I didn't mean to start a Toughness vs. Anticipation debate, though sure you can discuss if you like. I just wanted to correct the misconception about Toughness being less effective the more armor you gain, it actually gets better.

This was the first thing that had been proven about wow mechanics, on conquest boards back then; about 2 years ago. And as the armor bonus from toughness increases with value, it is obvious that it scales well. I havent heard anyone talking about 'preferring' anticipation over toughness. Defense, while it is indeed cheap and necessary to a degree, is not the ultimate stat you are looking for.

Here are some examples :
http://cqforums.negumi.com/viewtopic.php?t=470&start=0
http://evilempireguild.org/guides/diminishmath.php

There is another popular question though, slow tank weapon or fast tank weapon?

Edited after the following post. It should have been apparent though, it didnt really need a rephrase.

Actually thats wrong, it does.

What doesn't diminish, however, is lifetime. Adding X armor to the amount you already have will always allow you to live Y more seconds against melee damage, no matter what you have before adding X (except for the cap once again).

There is, however, diminishing returns on damage reduction when adding X armor.

Take the formula provided. If you have 10k armor and add 2k more to 12k, this will reduce all damage you take by 8.35% (aka. an attack that hits for 1000 on 10k armor hits for 916.5 on 12k armor). Add another 2k to that (from 12k armor to 14k) and the reduction you will see is only 7.7%, aka. an attack that hits for 1000 on 12k armor hits for 923 on 14k armor. So even though we added 2k armor in both examples, we gained more direct reduction from the 2k when they were added to 10k armor than to 12k armor.

Personally i'm a fast weapon guy, love my kings defender and it does the job hopefully one day go back and kill geddon to complete my TF

Well, 2 posts up someone wrote:
So maybe not the wrong thread.

My experience is that speed kills. You get an outsized benefit from being able to dump all of your excess rage into more heroic strikes, more quickly when you're taking a lot of incoming damage. Sitting at 100 rage and generating more rage does you no good, being able to "dump it" down to a more reasonable level faster is important. With quicker attack speed you generate more dps from HS and generate a lot more threat per second from the higher dps and base threat on HS. A faster weapon also provides for a less spikey threat generation curve, but that's not as big a deal.

With the way devastate works, you're only getting 50% of the delta between a slow and a fast weapon. Realistically you're only going to get at most 2 devastates in a 6 second cycle. In that same timeframe I can get 1 more HS with a 1.6 weapon vs a 2.2 speed weapon (2.7 attacks with a 2.2 speed and 3.7 attacks with a 1.6 speed). The extra threat (pre armor mitigation) from 1 more HS per cycle is about 400 before stance modifiers and enemy mitigation. I don't think you can realistically generate 400 extra damage per attack from using a slower weapon (2 devastates at 50% damage). It's also worth noting that 193 of the heroic strike threat will count regardless of enemy mitigation. If you're offtanking, slower is probably better (and it's easier to shift to dps if you're using a slower MH).

As far as the whole anticipation vs toughness debate, I personally think you are better off with pure mitigation vs avoidance. Avoidance only scales with incoming damage, whereas mitigation will scale with your gear. Avoidance doesn't work if you're stunned, incapacitated, or facing the wrong direction. In addition, the incremental value of avoidance goes down as the % mitigation that you receive from armor goes up. Conversely, the value of avoidance goes up as the incoming damage goes up. E.g. your best "tanks" for Razuvious were rogues, thanks to the fact that you couldn't conceivably soak the hit.

1 skill of defense (or 2.4 defense rating at 70) is worth 0.12% avoidance (dodge, parry, miss), so the anticipation skill is worth about 2.4% of total avoidance (not counting avoided crits or blocked attacks). If you assume a warrior has about 55% armor mitigation, that avoidance translates to 1.1% less damage taken through a cycle because unavoided attacks would have been soaked by his armor. Block value will increase it a bit, as will the ability to negate crits (if you aren't at 490 defense). There really isn't a lot of value to being over 490 defense since you could probably get pure +dodge rating or +parry rating cheaper.

All that said, I took both toughness and anticipation. It allows me to socket my slots with mostly +12 stam gems and allows me to use other forms of avoidance on my gear other than pure +defense rating. There really isn't any kind of trade-off between the two talents in my mind. If you're serious about pure tanking, imp bloodrage and tactical mastery are lower priority than anticipation.

I currently have toughness and anticipation.
If I can get to 490 defense without sacrificing the other stats that I have, anticipation is the first thing that I'd drop, as there are so things I truly miss having (piercing howl).

I took both aswell. No reason not to if you're going for full prot spec. I imagine the choice would be a bit harder if you're going for a hybrid build but there's no real beneficial talents you miss out on if you spend 5 more in that if you're going for full prot. The extra avoidance is nice and mostly the main reason. I'm sitting at about 517 def I believe. Of course going for dodge rating would be most beneficial for the itembudget, it's not really an issue til we can build items ourselves anyway. At 21% dodge 17% parry and 22-23% block/310~ with 12.2k~ armor with 'raiding gear' (from head, not logged on). If I only could pick one I'd probably go with toughness unless my def was lacking, however anticipation works against elemental attacks aswell, which is a nice side effect, something that extra armor does nothing against.
As for weapon speed, it doesn't matter that much, you can dump all your rage moderately fast anyway, besides, almost all tank weapons are fast in TBC. I prefer fast though.