i hav played both mods XL and BKB, i think BKB is better as it has a more variety of factions, but when i installed BKB the factions were there on the list of factions i could choose from but no descriptions for them nor map to see where they are. so i had to go to where it was installed and it wasnt installed in the right areas in the vi folder. even though when i set it to be installed in C:\Programs Files\Total War\Medieval Total War so i had to put the folders that were in the installation in the right places in order for the mod to work.

XL seemed to work fine but not enough variety in factions to choose from but its still just as good.

Also there is a mod for BKB called the DUX mod which is multiplayer mod for BKB. i havent stopped playing DUX yet since i installed it who needs campaigns.....