Durometer? What the heck does that mean? Durometer is the degree of hardness of a wheel. The higher the number (i.e. 99a) the harder the wheels is. Obviously then the lower the number (i.e. 78a) The softer the wheel is.
What wheels are best for cruising? For cruising you want minimal slip and the most grip so the softer the wheel the better.
What wheels are best for carving? For carving you want a soft wheel with good grip that will release when you want it to.
What wheels are best for sliding? For sliding the harder the wheel the better. The harder the wheel the easier and faster it will release into a slide.