Unless you're only planning on playing one of them, I'd start with the first game, as there are some plot connections and returning characters. The story in the first game is very BioWare, while the story in the sequel definitely feels more like something Obsidian would come up with, but they're both fine.
Make sure to install the restoration mod for KotOR 2. I have no idea what it adds, but it has to be better than the original ending.
I thought KotOR felt like the missing link between Baldur's Gate and Mass Effect, but it's been years since I played it now.