That's tough. My several paragraphs may make some think I'm crazy. This could be a one word answer. but it is not that simple for me. I have given it some thought. The biggest problem for me is that I like military history as a whole, although, and of course ACW is my favorite, for history and toy soldiers.
The easy thing for me is WW2, but I have already begun that, somewhat. So that does not answer the question.
Napoleonic would be the second thought. But ACW tactics are so similar that it would take on the same view as what I already collect.
Some of the Western/ American Indian war figures are cool. I have some 30 year old Indian figures that I love.
I really like the Samurai era as well!!
BUT I like the Roman/Ancient Greeks/ Medieval time too!!
OK...I do not know!!!!