My advice - is just choose - I do not think it really makes a huge difference. but Make sure that you stick that type from then on out - for ever and ever.
My personal preferance is Ball lock, but I was given 4 pepsi soda kegs and so I had that as my base, and have bought 5 more since then.
Check your local HBS, find out what they sell most of - and what repairs they have, and then go with that model.
Kilroy