Popularity is regional, so you're going to have to find local historical players around you to answer that question.
I like Dux Bellorum by Daniel Mersey. It's part of the Osprey Wargames Series so it's widely available through book distributors.
http://boardgamegeek.com/boardgame/88079/dux-bellorum
It's a simpler game that plays fast. It uses elements with the number of figures not really mattering, so just use as many 6mm miniatures as you want on a base and adjust your base sizes based on your table size.
http://www.amazon.com/Dux-Bellorum-Arthurian-Wargame-Wargames/dp/184908680X/ref=sr_1_1?s=books&ie=UTF8&qid=1411254243&sr=1-1&keywords=dux+bellorum
For Napoleonics, it's a matter of what scope you want to cover. Tactical where you are manually forming battallions into different formations? Or perhaps a grand tactical level where each maneuver element is an entire brigade and you are refighting an entire battle rather than a subsection of it?