As much as I like spirit the paladin has his own healing and blessing of wisdom, spirit doesn't seem to be so big an issue.
That said I'd go with
Sta - HP keep you alive, a living paladin is always a dangerous enemy
Str - Allows you to kill faster, killing = leveling
Dex - Armor and crit chance, always nice
Int - Never want to run out of mana for heals, for the most part the paladin never runs out of mana if he's doing serious healing though