One of the most difficult decisions to make as a Protection Paladin comes in the area of Glove Enchants. There are two enchants that appear to be strong choices for adding threat: 20 spell damage, and 2% more threat.
So which one is superior for a Paladin tank?
Luckily, those fine folks over at Maintankadin have the skinny on this question. Check out the entire thread here: http://www.failsafedesign.com/maintankadin/viewtopic.php?t=7257
The thread actually examines every possible enchant you could put on your gloves.
For the cliff notes version : 2% threat will grant you more aggro than +20 spell damage as long as you are generating more than 500 TPS.