Check the weight rating for each and make sure there is some sort of warranty. Then go with the cheapest one that meets your requirements.
As a side note, if you intend to store the cars on the wheel dollies then it may be imperative that you get a dolly with steel wheels. Otherwise you will end up with some deflection in the dolly wheels over time.
I ended up going with what I wasn't going to go with initially. The first pic. They have a good load rating, and easily replaceable casters, easy to find....a 4-bolt plate instead of the other, a single stud with smaller wheel. Both had steel wheels but might as well spend a few bucks more on this investment and have them last. For warranty I'm not too concerned, it is princess and even a year or two down the road they'll still give you something to replace with.
BTW princess has them for $28 /pr. and the other as in lower pics up top for $18/pr....good time to get some for your winter projects, or just keeping the garage better organized for space.