How much room you need will be one factor to consider. While I have seen 40' travel trailers, those made for actually traveling much rarely exceed a 34' box length. There are still some smaller fifth wheels being made, but it seems many manufacturers smallest models are about 30'.
Many travel trailers are marketed to entry level RVers with weekend and vacation use in mind. They are generally at a lower price point than fifth wheels. Insulation is often minimal although there are some that claim to be four season insulated. This may not be important if you can travel with the seasons. Travel trailer construction is also often done with infrequent use in mind, although there are some well constructed makes/models out there. Cargo capacity on many especially the light weight models is relatively low.
As mentioned, if you are trying to fit the RV to an existing tow vehicle, a travel trailer will put less weight on the tow vehicle 10-15% of trailer GVWR compared to the 20-25% of a fifth wheel. With a good weight distributing and sway control hitch like a Hensley, Pro-Pride or Pull Right, trailer sway in cross winds and even from trucks passing at 80MPH is not an issue.
Good Luck with searching for and finding the right RV for you!