Fatimids would be a better choice for two reasons; both Ayyubids and Abbasids were actually vassals of the Seljuk Turks; both of them were sharing the same branch of Islamic faith, Sunni, while Fatimid Caliphate was Shiite and they represented everything that was 100% opposite to the Sunni legacy.
The ideal would of course be to include them all, but since you have a certain hardcore limit, then it is my belief that Fatimids are a better choice both geographically and culturally.
EDIT: since the game is covering 1099-1400 period, a more generic term would be Arabs or Saracens, but this is a little tricky.
- Abbasids were Arabs, but they were completely annihilated by 1250. Capital city Bagdad.
- Fatimids were also Arabs, but of Shiite faith, and were annihilated by 1171. Capital city Cairo.
- Ayyubids were Kurdish/Turkish and survived only between 1171 and 1250. Capital city Cairo.
- Mameluks were Turkish and ruled Egypt between 1250 and 1517. Capital city Cairo.
- Zengid Dynasty was a Seljuk Turkish state that ruled over Near East between 1127 and 1250. Capital city Mosul and Damascus.
Since you are including Turks, it would be difficult to pick a second name among the ones listed above. Fatimids are a good choice for 1099, but they only last less than 100 years in your scenario. But then, this is just a game, so you come up with whichever sounds best to you.
