Rome, Followed by Shogun 2. Rome has more unique units, better setting, more factions, etc.
Shogun 2 has the benefit of hindsight. EVERYTHING is more polished. The diplomacy isn't a joke, reputation matters, the AI is semi-competent, trade with other factions actually provides a noticeable income, technology can be researched, generals earn skill-points, and on and on..
And now, we will have Rome 2, which will have all that PLUS the setting and factions with unique units.
And it will be awesome.
And it will be awesome.
And it will be awesome.