I voted musketeers. To be honest I don't think any of the UUs are a huge improvement over the stock musketmen, but I like musketeers the best. When I build muskets, Its mainly as a complement to cannons. Cannons are so strong that you don't really need any extra strength in the musket to clean up after them, so the Janissary is sort of a waste (the +25% against mounted is useful, but it's easy enough to use pikes instead). The Oromo is nice since it can sometimes win battles without taking any damage, but even at drill 4 this rarely happens.
What musketeers do is let you have MORE on the front line, at all times, then you would otherwise. A musketeer will be there, ready to fight, while other units are still moving up from the city where they were built. Admittedly they still have to wait for seige, but you can move the seige while the musketeers heal, and then catch up later. Or the muskteers can pick off stray units and move back, or pillage and move. But mostly you just end up with more units at all times.
I imagine musketeers would be good in MP too, especially with a city elimination limit, but I've never tried it.