Builder a halfling charger is actually pretty good.
The lance is designed to be the best weapon for this, you just have to understand where the damage comes from. You're gonna want flat bonuses, so a paladin or a cavalier would be ideal. I would'nt worry too much over STR being the highest it could possibly be, so long as you get enough for Power Attack. Investing into a 14 would probably be the sweet spot.
Building for the lance can give you some of the best consistent damage in the game, but I would make sure you take a mount that is maneuverable. I would focus on the Spirited Charge chain for that sweet triple damage. Ultimately, you'll want one of these, as it saves you money from having to invest in your own STR, and you can instead focus on your mount's.