Well I'm not sure why you are painting the floors (as opposed to staining). I don't think the paint holds up as well, regardless of wood.
I agree to stay away from pine which is soft. We've had good luck with oak. Oak accepts stains well and due to the strong graining, it hides scratches better than some other woods. If you are staining, be sure to use 3 coats of poly. Lighter stains tend to show scratches less.
You could also use hickory which is harder and also has strong graining. Some of the exotic harder woods (e.g brazilian cherry, brazilian walnut, brazilian teak) are harder but show scratches more.
Debbie Gartner, aka The Flooring Girl
http://TheFlooringGirl.comWestchester County, NY