[Saros]

I wouldn't say that a Cleric kit dualled to Fighter or a Fighter kit dualled to cleric can be more powerful than a single paladin kit. Paladins can become pretty hard to crack later in the game, with the combination of Armor of Faith + hardiness + defender of Easthaven. In addition, Paladins can use powerful bladed weapons, and Carsomyr for dispellation/magic protection.

I wouldn't however put Inquisitors as 'most powerful' of all paladins. They have True Sight and Dispel magic, which is nice, however they lack Armor of Faith and Draw Upon Holy Might, which is bad. I think that the second two options are better for a solo (better fighting skills and resistances) as well as for a party Paladin (because Dispel Magic is often impossible to target in such a fasion that it affects only opponents).

IMHO the best Paladin kit is the Cavalier, because of the nice immunities and bonuses with almost no drawback.