C.C.R, go with the pine but distress it so that when something is dropped on it in the future the new dent will disappear in the sea of other dents. The southern yellow pine is harder that white pine which is what I lay. The flooring should be laid perpendicular to the floor joist.
Make sure to have the air conditioning on and have the wood in the house about a week and a half before installation to acclimate to the temperature and humidity.
They also need to know that the humidity in the house needs to be maintained at between 35 and 45% or else the flooring will cup or shrink.
I've got a couple that have small children that ride their tricycles on the wood floor and to date no visible damage yet, and that is white pine.
The other option is to put in a rough sawn wood floor. These have been very popular of late and I have been installing and finishing several. I've got one that is 2700 square feet in a million dollar home coming up in about 4 weeks.
Here is a picture of one of my distressed pine floors.
Dave.
edit: I didn't see your post about the second floor subfloor being the 2 1/2" thick. I would just sand and finish it, if it's pine and not plywood.