Depends a lot on your wants and needs - how many people and how they get along when space is limited (you will be in only 250-300 sq feet).
The less expensive trailers won't hold up well under everyday use - they are designedd for vacationing, which translates to 2-6 weeks per year of actual use. The more expensive brands will generally have better materials and construction and so will last longer under heavy use.
I'd pick aluminum frame and fiberglass exterior, but there is no strong reason to insist on one over the other.
Good brands? Dozens & dozens of them, but not every model or series of each brand is automatically "good". Some I would recommend are Jayco, Arctic Fox & Nash, Holiday Rambler, Golden Falcon, New Horizons, Newmar's trailer line, Carri-lite, and Alpenlite.