Return of Reckoning

I've used Ritual of Lunacy with the AP Regen talent. It's good, but you sacrifice Aethyric Shock and a lot of points on the Alchemist Path (making single target heals worse). It just doesn't seem to be worth it.

How does the Sentinel and Oppressor armor sets compare?

It looks like you could get an additional 2% block with Sentinel (Helm) but you'd be trading the Endure bonus for Arise (stun/knockdown immunity proc).

Which proc would you prefer? Is it worth the additional block?

Edit: How valuable is ...