Another vote for Impetus. Tried most sets over the year – like the mechanisms and the non-IGO UGO activations. Tried Hail Caesar, which has much to like, but for me (personally) it didn’t do pike formations well (my main period), didn’t like double width large formations (instead of double depth) and Imperial Romans seemed either under pointed or over powered against natural barbarian enemies IMO.
For Impetus I love the large bases for a single unit and the play is faster than FOG but has a little more depth than HC.
Just my thoughts – no right or wrong – its all down to personal preference 😉