Yeah, Turks dominate! Easily my favourite faction. They can run rings around almost everyone. In my opinion, the only major problems they can face are armies of heavily armoured Christian elites defending on their own ground. An aggressive Mongol horde that charges in (as opposed to skirmishing) will also overrun them sometimes.

Apart from Janissaries, the Turks aren't "tough" so much as skilful and fast. Oh yeah, and almost everyone has a bow - bonus!