Ball lock are taller (25" w/o disconnects; ~27" needed w/ disconnects)
Ball lock are thinner (8.5" diameter)
Pin lock are shorter (22" w/o disconnects; ~25" needed w/ disconnects)
Pin lock are fatter (9" diameter)
There are such things as CONVERTED pin lock (i.e. pin lock kegs converted to ball lock)
These would be the shortest (~24" w/ disconnects) and fattest (9" diameter)
maybe this is what nateburn has?
If you have a vessel where you will put your kegs then it's time to get measuring to determine which size kegs will maximize your efficiency in regards to space utilization. However, seeing as you just picked up a couple then I'd roll with what you have. My fridge is vertically limited so pin locks were my best option, however I can only maximumly fit 5 kegs whereas with ball locks I could have fit 6.