With some of the changes to paladin tanking mechanics in 3.0 to bring us more in line w/ other tanks, I believe enchants in favor of strength should be priority if we use the figures at elitistjerks & the maintankadin forums:
1 strength = 2 attack power
2 strength = 1 shield block value
1 attack power = 1 spell power
Meaning Strength could be considered more important than Spell Power in regards to single target threat.
However, in AoE tanking situations, Spell Power is still king.
Figured I'd throw this out there seeing as Strength enchants are rated as a 0 here for Tankadins.