If you go with a pike and musket type of army with musketeers and ashigaru, you'll get some challenging battles. You can defeat most armies but you have to be really careful with your maneuvering. It makes for longer battles, but it can be really rewarding when you defeat an all samurai army with a mostly peasant army.
Also it's a really cheap army.

But, on the other hand, it's also really fun to build an elite, expensive army of samurai and just sweep everything in your path.