Shashka. For all that people say it is crap, my 21/15 can use it rather well on foot or mounted. For the price (more important then ever with the new upkeep and expensive cav) it has good speed, amazing length, good damage and looks nice (besides the hilt... I am talking about the blade).
Also, less people use it so you can surprise a lot of people with the length.
Did I mention that it also has a sexy name?