I recommend 1 in throwing or bringing a light crossbow with yourself... thats often enough to get a lancer (horse) or a 2h with long reach to leave you alone or to kill them slowly. Especially letting a lancer come towards you, hit him once so he twitches and then when his horse stops next to yours, just laugh and bash away at them.
If you are fighting vs a lancer as 1h, I´d normally go for the horse first and you really have to use your shield/speed to give yourself a advantage over his reach (the slower you both are, the better... just keep turning around him till you are both slowed, then stick close).
For weapons I found the italian falchion to be a perfect weapon if you get dismounted a lot (works well even without a shield) and for a lower level.
The Arabian cav sword has good reach, great swing damage and workes really well vs other riders (and there horses) - you might have to hit a few more times, but it is a good weapon mounted and dismounted.
The steel pick is for a very unthankful and hard role, but game winning - hit the biggest tincan you can find and watch them die to 33 p - this needs some training, since it seems to be by far the hardest weapon regularly used (by me) to hit with from horse, but after a while you just have the "bump to de-shield-strike" timing down.
The WarHammer works especially well on a higher str build and really works well vs everything, though it does suffer if you are dismounted - suprise enemys with the high reach of it´s piercing attack, but go for the kill with a swing - learn when you can stop to keep beating at a downed enemy and when it´s time to move on (lancers/inf incoming).
The most easy victim for the mounted 1h/shield player would be archers, 1h (shielder) enemy inf, especially the later will soon have nightmares about your shield bumping charges. You are far better off if you get dismounted then that lancer and the shield really helps vs the 24/7 archer/x-bow spam.
