I think it all depends on your priorities and budget. If you want new kegs and stainless QD's, ball lock is the only way to go.
If you are buying used, you can find both. If you have specific space constraints, you may need to go one way or another.
If you are looking for the best deal, you may end up with both!
I have a mix of both, probably around 60 pin lock and 30 ball lock. I live in Atlanta though, so pin lock has been a lot more prevalent, at least when Coke was moving away from kegs. I find them both interchangeable for my uses, and I have dozens of sets of each QD. I did want a stainless QD for a side project, and in all my years of brewing, I've only ever been able to find a single stainless pin lock QD, whereas stainless ball lock ones can be found just about anywhere online.