Arab cavalry has nice length, but rather poor pierce (19). If you're going for a shielder, (or 1h+sh on horseback), then I'd suggest a weapon with more pierce on the thrust (long espada does rank pretty highly there), or a sidearm (steel pick, warhammer, and iberian mace are all weapons I have seen perform rather well) in dealing with well-armored opponents.
Of course, you could always be a man and get a great lance, and only couch, even on footback.