I happen to use both. They each have advantages and disadvantages.
Pin type keg advantages:- Shorter than ball type, so they fit in keezers and kegerators that are shorter in height.
- They usually cost about half of what ball type cost. At least that is the case were I live. The going price for pin type here is about $40, compared to $80 for a ball type.
Pin type keg disadvantages:- Fatter than ball type by about 1/2 inch in diameter. Not as many may fit, compared to ball type.
Ball type keg advantages:- Not as fat as pin type, so sometimes you can fit an extra keg in a keezer or kegerator if using this type.
Ball type keg disadvantages:- Cost is usually twice the cost of a pin type.
- Taller than pin type, so they sometimes won't fit in a keezer or kegerator because of height, even when width isn't an issue.
I personally use both types in my keezer. I have a 7.2 cu/in. chest freezer that I converted into a keezer. If I were to use all pin type, I can only get four kegs into it. Three on the floor and one on the shelf.
By putting three ball type kegs on the floor, the extra space saved from the narrow diameter of the ball type, allows me to have enough room to get two pin type or two ball type on my shelf, instead of just one. That allows me to have five kegs in my keezer, instead of just four. With three ball type on the floor and two pin type on the shelf it's a tight squeeze, but it works.
By using the pin type for my shelf kegs, I save $40 on each pin type and just squeeze them in.