I bought the microsizers Tire Kit, and I ended up using the mediums.
The "soft" tires are grey, and try to simulate a tread, but they aren't that soft, and all the tiny bumps just mean reduced ground contact.
The "Hard" tires are pretty hard, and ribbed, again with a reduction in ground contact.

I don't like how the grey tires look either.

These are just personal preffs, mind you.