Hi there, I'm a tank just getting into 25 man content with my guild. However, I'm starting to feel the crush of indescision on what kind of gear I need to be focusing on. The information is there, but sorting through the millions of guides and forum posts is a little overwhelming. As of now, I've been focusing on EH exclusively (with the exception of the autoblocker which I love), but I'm concerned I'm missing out on avoidance and aggro gear, which I've mostly ignored in the name of EH. I don't want to snag gear from other guild tanks unless I'm certain I'm benefiting. As a note, I've also had crap luck on weapon and shield drops - the quickening blade just dropped last night, upgrading from Warbringer. I keep Grom'tor's for heavy mitigation fights, but no luck with defender or sun eater.
Evaluate what your primary function is while tanking. If you're the progression main-tank, focus on EH and expertise, and make sure your hit isn't awful. This isn't a big issue since most of the good EH pieces also have expertise (badge neck, bracers, and the 2.4 belt).
If you're ever the main tank on a fight that needs high avoidance (ie, Prince in Kara), then don't ignore high-avoidance items either. Usually for me, my high avoidance items are things that I have since upgraded to better EH/threat pieces, like the 2.3 badge belt, maiden's neck, Nightbane's chest, etc.
If you're also doing a lot of trash main tanking, then you'll want a full threat set. Focus on hit, expertise and shield block value (if you have to choose, IMO SBV is better for trash clearing than the other two, but a good balance is best. I have ~550SBV, 27 expertise and 110'ish hit for my trash-clearing set). HP isn't as big of an issue here for the most part, at least not in the 10mans that I've been doing. I don't have much experience in 25mans, so I'm not sure how that affects you.
If you're primarily the off-tank for either trash or main fights (like High King for instance), I'm not sure the exact gear makeup you'll want so someone else can correct me if I'm wrong, but I think the focus there is that you don't need to worry about threat at all, and should focus on avoidance and EH. If it's a fight where you offtank something and have to switch to DPS mode without dropping combat, though, I have no idea what the best gear makeup is for that.
Lastly, if you're an offtank who will have to switch to ProtDPS, you'll want to get a decent fury-like set. Get 9% hit and then stack attack power and armor penetration. I wouldn't ever take these items over a fury warrior, myself, but it depends on how much you have to be in this role.
Overall, though, maybe you should talk with your other tanks about potential items that would drop that you're interested in, and find out if they want it as well, and why they'd wear it. As a tank, you're gonna need multiple sets of gear, and so you shouldn't gimp yourself by letting all the other tanks build their EH/DPS/Threat/Trash tanking sets, especially if you're not on a DKP system.