my favorite missle mercanies has to be the cretan archers, belaric slingers...
couple of battles in gaul or iberia and they kill those nasty barbarians like flies getting zapped...

in the africa, nothings better than the numidian calvalry, theyre just so... good !

In greece... has to be the mercanary phalangitai or hoplite, i mean, you just cant resist good old hammer and anvil on those rebellious greeks

thrace...
falxman (drugonitzasaijajs sumthing like that) 'nuff said

then from here to the far east baktria, its all phalangitai/local calvalry and infantry.

favorite 3 mercanaries are phalangitai / hoplite / cretan archers