Personally, I think whatever you get, buy it based on how convenient it is for the initial buy in. Like, if you can get 8 pin locks for a good deal, and pin locks look like they will be available for a while from your supplier, go with them. Same deal with ball locks. The two kegs have physical differences as far as width and height, but this is only an issue if your freezer or kegerator is constrained in width or height.
I like ball locks because the seem to have more accessories and they are more easily obtainable at my lhbs.