For those who are wondering which of the titles you should get.
It got so far the biggest mods compared to the other two and still got a huge big community with more mods coming out.
It's mostly for those who want a Single-Player RPG Sandbox but it's Multi-Player is decent.
2. Warband + Napoleonic.
For those who are more interested in the Multi-Player part of the game than the Single-player.
3. Fire and Sword.
It's a little further into the modern era with guns and things like that but it's in my opinion far from an improvement to Warband.
4. The vanilla game.
It's for those who desire the older mods that haven't been updated for Warband.
Suggestion on Mods:
I prefer Prophesy of Pendor (A little harder than vanilla) and Floris Mod Pack (Great compilation of mods) for Warband, they add great features and a lot more content.
-Addition- Blood and Steel for Warband. I used to play it a while back and if I remember correctly, it's a great mod.
NexusMods - http://mountandblade.nexusmods.com/
TaleWorlds Forum - http://forums.taleworlds.com/index.php#c5
Mount & Blade Repository - http://www.mbrepository.com/
Good Luck & Have Fun