Just make sure the wheel diameter is way bigger than the size of the floor surface imperfections ...
Typically the Colson 3 1/2" x 1 1/4" red polyurethane casters are the standard for racks, and their 4" x 2" versions the standard for larger and heavier cases like cable trunks.
Larger is better if you can afford them.
I've got some cheap 5" x 1 1/4" casters on 1/4x1/2 flat dollies that do handle the cracks and thresholds better, but the downside is they haven't lasted as long as Colsons(buy once, cry once), and they don't handle as much weight as a similar Colson.
Best regards,
John