One of the changes in 3.0.8 was a buff to the Tempered Titansteel Helm, adding a Meta Socket and a Blue socket with a Defense Rating socket bonus.
So let's compare it to other helms around it's level. We'll compare it to the Armored Titanium Goggles, Thanes Tainted Greathelm, Platehelm of the Great Wyrm, T7 and T7.5.
In most of my analysis you will see I disregard 'threat' stats like Strength, Hit and Expertise. This is done with the belief that threat is a minor issue right now. Gear decisions should be based on Survival stats alone. You'll get 'enough' threat stats that come along for the ride.
Also each person has to evaulate the chioces based on their gear.
Armored Titanium Goggles
This is the Engineering only helm that you can craft use as early as 72. The trade off here is 12 Strength, 14 Defense, and 43 Expertise for 51 stamina. The Engineering helm has a yellow socket instead of a blue with an Expertise socket bonus. I wouldn't try to gem the Engineering helm for the socket bonus.
As long as you can afford the loss of 14 defense, I wouldn't use the Engineering helm. It seems the intent of the Engineering helm is get your from 72 to 80 where you would replace it with the Titansteel helm. This is odd because you have to buy mats that only drop in Level 80 content (Frozen Orbs) and power level your Engineering to 440.
Thane's Tainted Great Helm
This drops from the 4 Horsemen in Naxx10. Using it you gain 12 Str, 39 dodge, and 44 Parry at the loss of 51 stamina and 6 defense. Thane's has a yellow socket versus a blue for Titansteel.
I think what is clear here is the choice between Thane's and Titansteel is what my buddy calls Armina (Armor plus Stamina) versus Avoidance. Thane's is clearly an avoidance piece while Titansteel is an EH (Effective Health) piece. So you have to look at the rest of your gear. Do you need more stamina or more avoidance. I think where the two pieces are offered works quite weel. When you are a new tank, a fresh 80, you need the Effective Health to try to meet the minimums of the encounters. Once you've gotten into Naxx a little ways (and 4 Horsemen is near the end) you probably have 'enough' Effective Health and are starting to look to increase your avoidance.
I think if I had Thanes and Titansteel, I'd wear Thanes for most stuff, but Titansteel for Dragons.
Tier 7 Heroes Redemption Faceguard
The difference between Tier 7 and the Titansteel is you gain 11 Strength, 74 Block Value, and 30 Expertise for the loss of 51 stamina and 3 defense. You also have a less desireable Expertise socket bonus on Tier 7 compared to the Defense socket bonus on Titansteel.
This looks like a Stamina versus Block Value choice. There are times and fights where I want the Block Value helm (fast, light hitters, AoE situations, etc), and times when I want Stamina (slow, big hitters, Dragons). So as crazy as it seems Tier 7 for Trash clears and Titansteel for Bosses.
Platehelm of the Great Wyrm
This drops from Sapphiron in Naxx25. Using it you gain 39 Str, 2 Defense, 38 Dodge, and 67 Block Rating. You lose 11 stamina and the sockets (meta and blue). You could gem the Titansteel Helm with Defense to make up for some of the Block Cap loss from the 67 Block Rating.
This happens to be the helm I'm wearing in my current gear. It's tempting to change it out for the new Tempered Titansteel Helm just because I'm fighting so hard to stay at the Crit Cap (540 Defense). I could socket the Titansteel Helm with Defense and open up a lot of freedom in the rest of my gear.
Tier 7.5 Valorous Redemption Faceguard
Okay so the last hat we will look at is the Tier 7.5 from Naxx25. This, like the Platehelm of the Great Wyrm actually has a higher item level than the Titansteel Helm.
What's the extra item levels grant you? 19 Str, 77 Block Value, 20 Defense, and 35 Expertise. You also get an Expertise socket bonus, and you still give up 35 stamina.
The analysis hear is two fold. First of all, do you need the 20 defense to stay at the Crit Cap? If you do, you need the Tier 7.5.
If you don't it's a question of nearly 90 total block value (when you factor in BV from Strength) versus 35 stamina. You would only need to get hit 4 times for the BV to come out ahead. I have to think in this case that the Valorous Redemption Faceguard would be used in all cases over the Titansteel Helm.