My gut, given your concerns, is Mongoose.
I'm not sure if you've seen Theck's new numbers, but here's the big discovery: The change in patch 3.2 that made Seal of Vengeance a physical attack (arguably so it worked off the melee hit table and not the Spellhit table) also allowed it to proc chance-on-hit PPM effects. Paladin uptime for mongoose has gone up SIGNIFICANTLY as a result.
Mongoose is now one of the best threat enchants, only slightly behind Accuracy, along with obviously bringing some real avoidance/mitigation benefits.
As to your concern of stacking procs on procs, the more procs you stack the more likely SOME of them are going to be up at any given point of time.
Mongoose, while not the best avoidance OR threat enchant, now appears to be one of the best if not the best overall itemization value enchants for paladins - similarly to how most of us have switched to Agi/Stam in red slots instead of dodge/stam. Double dipping is HUGELY valuable when you have limited slots.
goose it up.