King Keg top tap barrel has a float system inside. It draws the beer off the top which is supposed to allow you drink the beer sooner!
Same as the bottom tap keg except the tap is at the top! Why is it different? Well....
The top Tap King Keg - The top tap means the barrel can go at the back of a shelf. The bottom tap barrels have to hang over the edge of a shelf or you can't get your pint pot underneath.
The big trouble is that it depends on the gas pressure to force the beer out so it's heavier on gas and if you run out of gas you can't get the beer out!
I'd always go for a bottom tap barrel unless you really need it to go at the back of a shelf or on the floor.