I would 2nd the suggestion to go to an RV show. There are soooo many options when it comes to travel trailers. A show is a good way to investigate the many options versus running around to see individual trailers.
Regarding used versus new, unless you're well versed in things mechanical (I'm not) I'd go with a new unit with a good warranty. A travel trailer is a combination of home and vehicle. Unless you feel confident that you can do a thorough inspection of both I'd shy away from buying used unless it's used with an extended warranty that can be transferred.
Enjoy the hunt :).