The Sarranids never looked like they had good infantry to me, what am I missing?
Personally my favorites are -
Nord Aetheling line: Powerful throwing weapons, solid 1h with polearm option
or Rhodok Capitano Di Ventura line: Very basic but tough and effective at earlier tier(4-6)
Slave Crushers: Fast to level, blunt damage + bonus prisoner management makes them excellent)
Khergit Numyn Ad: Fast to level(Can get them by just trainer skill by level 22 IIRC), decent melee capability w/shield, and reasonably fast piercing damage bow
or Rhodok Condottiero D'Assedio: Obviously the toughest archer, high piercing damage crossbow, durable shields, heavy armor and a good one hander
All depends on what I'm using them for of course. The Rhodok Fante/Veterano/Di Ventura are very durable for their tiers(4/5/6) and are great for castle defense or just blocking your archers. Aetheling line is fairly versatile offensive infantry, good for a siege since they can break through fast get your archers in. Slave Crushers are mainly for beating up other heavy cavalry by having them charge at their flanks when they're closing in on my infantry - or of course just beating up bandits for prisoner money. Numyn Ad is one of my favorite things to just stock up on since they rain arrows on things but then aren't absolutely worthless when they run out of arrows either. D'Assedios are just amazing if I want to siege a castle by attrition and just camping outside hammering the defenders shields up or not with slow firing but high damage crossbow fire.
Of course, I am cherry picking from all factions. I think if I had to pick a single faction, and actually planned on using its cavalry rather than just manhunter types, I'd use Vaegir. They have infantry with blunt weapons that makes it quite a bit easier when you're up against heavy armored troops, they have solid if very basic archers, and they have pretty good cavalry as well with horse archers if you really need them.