I'm presently considering three sets, though I may run across others I like as well. Nothing's set in stone, really, at least till I start basing for one set or another. :>
I think my front runner at the moment may be Shako (http://email@example.com/shako1803/index.htm). The rules make an easy read, and I really like the breakthrough rules at first glance. I also like the rules for artillery crews retreating and then returning to get the guns back in action. I'm tempted to allow artillery crews even in rout to be rallied (subject to the regular rally rules of course) and returned to the guns if their side still has control of that ground. I wonder how historical this is.
I'm also considering Grenadier (http://www.anst.uu.se/svennore/Grenadier/index.html), which looks interesting but perhaps a little complex for my liking.
The third set under consideration is Old Trousers (http://www.anst.uu.se/svennore/Grenadier/index.html) which I have yet to actually open and look at. The introduction looked interesting, but we'll see if the actual rules hold up under scrutiny.
Overall, I'm looking for rules sets that will give roughly 10-30 soldiers per battalion, which with my current troops on hand (not counting any an opponent brings) would give me roughly 3-5 cavalry regiments and anywhere from 20 to 60 battalions of infantry on the table, counting both sides.