Hi Emily,
I have a MacBook Pro but it’s only for when I am on the road. I stick small panos from a 10,5mm lens but when I do serious work, I use a MacPro. The latest ones are really great.
If you are producing large panos, go for the fastest you can afford. As much memory as you can. Most applications will be much faster with a lot of memory.
If you use PTGui, check this link for compatible video cards. http://www.ptgui.com/support.html#7_1
I had a 2010 MacPro and switched to the latest MacPro and a job that took 4 hours to stitch now stitches within 20 minutes… It was for a 105 shots pano (36 megapixels).
Good shopping!
Luc