You could, but having "Keen" on weapons isn't such a big deal anymore.
Some of the best Bastard Swords for Paladins (Divinity, the Morninglord's Goal most notably) don't even have Keen on them.
You're likely going to want Improved Crit: Slashing if you're going to use a Bastard Sword.
EDIT: See unbongwah's post below.