They are both the same volume, but as mentioned above, the pin locks (Coke style) are wider in diameter and shorter. You may need the skinnier ball lock (Pepsi style) to fit in your fridge or you might need the shorter pin locks to fit so try to work out your dimensions before you buy. Also, as mentioned, both are easy and neither is better, but ball lock fittings are a bit easier to find (same price). O-rings are cheap, easy, and mandatory to replace of course, and you can even replace the posts. You can put ball lock posts on a pin lock keg, and vice versa. One up on the make sure the main seal lip is in perfect shape because a new o-ring won't fix a dented lip. Another consideration is that the ball lock kegs usually have a pressure relief that you can operate manually any time you like. The pin lock kegs usually don't have this, but just a pressure based pressure relief system which is more for safety, not for convenience. I came across free pin locks so I built a 6 keg kegerator but when the fridge had to be replaced the kegs wouldn't fit so I was forced to switch to ball locks. The only real difference between the two (the pressure relief) made me happy with the way things turned out.