In terms of equipment, the Swadian Knights win out, since their secondary horse is a War Horse, as opposed to the Sarranid Mamluke's Sarranid Horse. Weapon-wise, Swadian Knights usually have two-handed swords, morningstars, lances, and heater shields, while Sarranid Mamlukes usually have elite scimitars, lances, two-handed maces, and elite cavalry shields. Armor-wise, they're pretty much the same. I doubt you'll notice a significant difference between the two in a siege situation, so it really comes down to which your prefer aesthetics-wise.