Mongol Khan's Guard. Since Mongols are Muslim they should be counted too...lol

I agree that Kwarizmian Cavalry pack major whoop-arse on their Catholic equivilants. However they are limited in number and can't be used extensively.

Christian guard are arguably the best there is to offer. However they're pretty hard to get as you have to climb up the tech tree, and one may not have the time for this if nasty crusades are bearing down on you.

Well. I do miss the Sipahi of the Porte units from MTW. If they were placed here in M2TW they would most certainly be the best the Arabs have to offer.