I like Byzantium pretty much. Some of their units are wonderfull as most of you know and permit you to fight with an equilibrated armies or legions on the early period.

However, as the game advances, I miss reliable spear units as the catholics have. You can manage without them or else recruit mercenaries but on certain armies I would prefer to have heavy spear units enrolled as regulars. Those facing a golden horde for example.

In all is a very interesting faction.

Also Spain is very attractive and with lots of resources, good position, good generals, nice tapas, good wine, marvellous food, sunny country, etc.