[Crenshinibon]

Well, why not establish a list of what you want?

The Ranger/Cleric:

Iron Skins
Simulacrum (Vhalior's Helm)
Easy early game.

The Kensai/Cleric:

Great THAC0 with ALL weapons (Harm, Energy Blades)
Has a difficult early game.
Has a very easy late game. (Can destroy most bosses with harm alone.)
Has a greater AC due to his class bonus.
Doesn't rely on ANY strength items for damage and THAC0, thus is free has a broader choice in weapons used and belts (Belt of Inertial Barrier).

Both have:

Four attacks per round.
Ability to get eighty five percent physical resistance.
Low AC.
No trouble with undead.
Team buffs.

I may have missed something, so don't take the list to heart. Both classes are very powerful, however, I'd view the Ranger/Cleric as more defensive of the two.

In a battle between the two, it's hard to say as to who'd win, as chances are, the Kensai/Cleric would land a greater amount of hits than the Ranger/Cleric, while the latter has Iron Skins to protect themselves from ten attacks, which, with Improved Haste, is roughly a round and a fourth (8.75 seconds, if it matters) worth of barrage.