Most of the bad units are the cheap and nasty ones that we expect to be. Like Greek archers or Celtic levies.

To my mind everything has its place if used well, but there are some troops that are suprisingly weak or inefficient in comparison to others around them. Top of that list for me is Iberian Medium Infantry as they are only marginally better than the Light Infantry for a lot bigger cost and are the same price as the Heavy Infantry which are stronger statswise.

Again, any type of artillery is rubbish value for money - and there are some pretty useless ship types out there as well, starting with the Trireme.