My mate's bearings spin longer - are they better?

The simple answer is "Not necessarily". Let me explain.

The difference between spinning the wheel and seeing how long it takes to stop and actually using the bearings during skating is the loading on the bearings. When you are skating, there is a lot of force from all of your weight on those bearings. When you hold the skate up, the only load is the weight of 1 wheel.

Testing how well the bearings perform with no load will not tell you anything about how well they will perform loaded. Try this (or at least think about it):

1. Build a flat bank that can be made steeper and shallower
2. Put a pencil on the bank, it's axis perpendicular to the slope
3. Raise the bank until the pencil rolls down the bank, and note the angle.
4. Cover a ball-bearing with grease and repeat steps 1 to 3

Which do you think will need the steeper slope? This is the one that would spin longer unloaded. Which do you think would roll better with 80kg on it? That is the one that would make a better bearing.

Basically, the resistance caused by lubricant is unaffected by the load on the bearing. The resistance caused by irregularities in the bearing surface will increase with the load. As such, with no load; lubricant drag is the dominant force whereas with a large load surface quality is dominant.

This is why the spin test is of no use at all in determining how well the bearings will perform when you are skating.