This is the main question to consider when making a decision. Most of the time, a cruiser is made to move in the street, on the asphalt, and as such, soft wheels are more adequate to keep comfort on the most irregular grounds. This is what we find on a large majority of complete boards which are precisely designed to be as versatile as possible.
If the range of cruisers complete boards often have wheels of duro 78a to 83a, it is not impossible to mount hard wheels on a Cruiser.
Hard wheels, and especially slide wheels, allow to modify the behavior of a cruiser to gain in maneuverability. In addition, the slide wheels have a better sliding capacity, so they are more adapted for tricks lovers and those who want to leave the possibility to go to skatepark. Finally, even if it's a bit more radical, the slide wheels are made for... slider! If you want to ride a freeride board to get around and have fun slidding, the choice is made.