If you're going to want to be buying new kegs, you will not be finding new pin lock kegs; pretty much all new kegs of whatever brand will be ball lock. Pinlocks tend to be about 20 bucks cheaper per keg, but see below, the cost may actually even out or be more expensive in the long run...
I had a mix of both in the beginning, kind of by accident, when I got a good Craigslist deal on a collection of kegs. 2 of them were pinlock, and I found having a couple of the pinlock form factor was advantageous for fitting beneath the blower assembly in my kegerator. I did also however find that the lack of a pressure release/pop off valve in the lid was annoying, and eventually replaced the lids. I can guarantee you that you *will* eventually press the wrong poppet (the liquid out post instead of the gas in post) and get a facefull of whatever is in the keg!
You can get generic lids that include the pop off, but they run 12-15 bucks each (maybe you get them cheaper on sale occasionally), which adds to the cheaper cost of the pinlock kegs. I've also slowly converted all my pin locks to ball lock fitting, which has also added to the cost of the pin lock kegs I have. I'm pretty sure that that if you're going to switch out the lid and convert the posts, it will exceed the price differential and ultimately cost you more, but if the size of the kegs is important for your setup, those are your options.
If you're going to be pinlock and only pinlock on your home system, and the lack of the manual pressure release valve in the lid doesn't bother you, the only other thing to consider is the popularity issue. If you were to take a pinlock keg to a homebrew festival or such, you'd probably have to bring your own connectors as well, and hope they have screw off connections on the liquid lines.