Any suggestions for a good size/brand of fire extinguisher?

Ever keen to learn, my dad has bought a propane welding torch. (He bought an arc welder too, but has no plans to use it anytime soon – one of those things where it was on sale at Harbor Freight.)
He’s asked for a fire extinguisher for his birthday, and I’m looking around for a good one to get him. I know to get an ABC extinguisher, but that’s about it.

Also, I’d like to get one for my sister, who’s recently moved into a small townhouse with a roommate and but a single exit.