As the ball locks are slim, it's easier to fit many of them in less floorspace than with pin-locks, but as pin-locks are short, there are probably more refrigerators and freezers that you could use with minimal/no modification for at least _some_ kegs. A lot of compact fridges you find on the shelf simply aren't tall enough, and if you only want to fit one keg, pin lock would be the easy fix- but if it's a couple inches taller, you might be able to fit 2 or 3 ball-locks there (provided the freezer/compressor hump allow)
I think it's safe to say that ball locks are somewhat more popular, so you'll see the kegs themselves often run $5-10 more apiece.