All Skateboarding wheels come in different color, styles, size and the diameter and durometer of the wheel affect the way the board rides. So both the diameter and durometer are pesonal preference and skatebording style, here is some information below:

What is the right skateboarding wheel for me?
Diameter:  Bigger wheels are faster and smaller wheels are slower.

52-55mm – Slowest, but great for tricks and small skateboarding riders
56-60mm – For beginners of all sizes.
60mm+ – There are for long boards, usually the biggest wheels.

The Durometer measures the wheel's hardnest, so the harder the wheels the faster it is, the softer the wheel the slower it will be but with better grip.
Note: Standard wheel durometer is 99A.

87a – Soft wheels are great for hard surfaces, they are used for long boards or street ridding. Your going to need good grip.
95a – Is a little bit harder and faster, but still got a pretty good grip.
99a – Both good speed and Grip and great for beginners
100a+ – The hardest and fastest wheel but not as much grip.