Ho-hum. The best way of upping TPS, is it?
Assume 800 TPS, 70% of listed damage from Shield Slam (20% miss, 10% crit, ~25% DR) and that Shield Slam is used every cooldown
1 Shield Block Value = .7 * 1.45 / 6 = ~.169 TPS
1% additional TPS = 8 TPS = ~47.3 Shield Block Value
That's equivalent to ~30.7 of any combat rating in item budget. Slightly shy of 2% hit, which is slightly more than 2% more threat given 20% avoidance.
Weapon skill rating is likely stronger still, although I admit I am more a little shaky on the mechanics here. Assuming 15 points of skill mean going from ~8% parry, miss & dodge on L73 to ~5% then 30.7 in skill rating is a little more than twice as good as the same amount of hit rating when hitting mobs from the front. However, I could be way off if skill doesn't work the way I think it does...
Anyhoo, point stands: if your goal is improved threat generation, get hit and most likely also weapon skill first. Block value is a nice hybrid threat/avoidance-stat, but certainly not the first choice for either in a raid situation.
Edit: For what it's worth, the TPS spreadsheet (
[Warrior] Tanking TPS sheet. ) is in agreement that both hit & weapon skill are preferable to block value for equal item budget, but I've no clue if it handles skill more correctly than I do.