Actually, the best weapon enchant for protection paladins is the old Potency enchant (20 Strength).
As there is no real mitigation enchant, weapon enchants are mostly useful for threat generation.
Mungo: 14,10 tps + 0,76 % dodge + 60 armor
Exceptional agility: 12,22 tps + 0,66 % dodge + 52 armor
Potency: 44,80 tps + 12,5 block value
Superior potency: 44,20 tps
Titanium weapon chain: 18,76 tps + 50 % shorter disarm effects
Accuracy: 28,75 tps
Black magic: ~ 35 tps
Mighty spellpower: 27,09 tps
I got these values from somewhere on http://maintankadin.failsafedesign.com/
but do not currently find it again.
The only enchant that is worth giving 15 points is the old Potency enchant. It does not only provide the most threat but also increases mitigation.