With Roman units I feel that I can out maneuver phalanxes with ease. When I play as the romans, I generally have just one type of army that I build, 12 to 14 cohorts of heavy infantry(Cohortes Reformata or Prinipecs), 3-4 units of kreten archers, and the general plus additional 2-3 cav units.. That all being said, the Seleucids roster is so diverse, you can create many different armies for many different purposes.