I’ve been mostly playing Impetus over the last couple of years, thought I’ve played a couple of games of Hail Caesar and am about to try the new Sword and Spear rules (which I’ll be reviewing on my blog when I do) which seem ok from a read through. I have my stuff on Impetus bases (80mm wide, variable depth depending on unit type), which can be used with any of those systems. I think Impetus is still my favourite, though as I said, I haven’t actually played S&S yet.
Over the years I’ve played a lot of different rules (started with WRG 6th ed, went through loads of others), and Impetus is the one I’d go for if I had the choice of game to play. DB* and FoG left me cold, I’d rather go back to WRG 6th again than those rules, if that helps give an indication of my tastes.