The Gallic Swordsman works perfectly for me. This UU simply combines the good movement of the Horseman, and the great attack/defense of the Swordsman! What else could I ask for? You can arrive quickly in your enemy's borders, you can run away if your unit is losing the battle, and it still have good attack AND defense!
What Arathorn said was right, though... it's a shame that, when you get Feudalism, this awesome UU is replaced by the lame Medieval Infantry...
You people can disagree, but when you are in a GA, getting a GS every 4-5 turns in almost every city you have, and suddenly they are replaced by the MI, in a huge map, and your enemy is very far, you really get annoyed with this...