I would say, if you think you might have need for a trailer for other things, get one.
If you know you will never need a trailer, get a dolly.
When I had a trailer, I used it for hauling hay, long lumber, rocks, etc. We don't have horses now, and I'm not much for big projects at my age, so no trailer any more.
For a dolly, I would recommend the American Tow Dolly or the Demco Kar Kaddy. The Demco is the best, IMO, but it costs more than three times what the American does, new.