I've only used ball-lock kegs because at the time I purchased them they were much cheaper. That was most of a decade ago, though based upon what Scott said things have changed since then. Last I checked it the ball-lock kegs have more than doubled in price since I purchased mine. Seems like I got in right when Pepsi was flooding the market.
I use a chest freezer with a Johnson Controller to hold my kegs. Based upon what Scott said I'd probably stay with the ball-lock kegs. It's easy to make a chest freezer taller, but you can't give it more floor area.