Sweboz, Aedui, Arverni, SPQR, Baktria, Kharthadashtim, Ptolemaioi (and othe successors), KH, Getai, Hayasdan, Casse are fun playing. Pontus, Saka, Lusotanann and Saba probably are less fun. Because they miss some key units or elements. Saba misses a lot, Saka miss low end payable troops and Lusotanann and Epeiros mis alot of regionals. (They both have provinces near them where no or barely any unit is recruitable.)