Wheel types.

[Snooky]

Hi all,
I recently bought a couple of second hand B4's, one for my boy and one for me. We have had great fun with them so far. Recently I took the wheels off to clean them and generally check them over, I noticed that one has what appears to be a 12mm hex fitting and the other is a pin set up.
So what have I got? Which is best? Is it easy to change to one type? Any input and opinions appreciated.

Cheers.
Snooky.