As explained above, the main reason a 5th wheel trailer is less prone to sway than a travel trailer is because of the location of the hitch. A TT hitch is about 4 or 5 feet behind the rear axle. The farther behind the axle the pivot point of a trailer is the more effect movement of the trailer will affect the tow vehicle.
A 5th wheel places its' pivot point directly above or slightly ahead of the tow vehicles rear axle. This means that there is less "leverage" for the trailer to affect the truck. Therefor, most 5th wheels tend to tow better than a travel trailer.
There are ways to alleviate this problem however. A Hensley hitch on the trailer projects the pivot point near the trucks rear axle so it makes the travel trailer tow as well as, and sometimes better, than a 5th wheel. As mentioned, tongue weight is also a big factor and should be between 10 and 15 % of the trailers weight. This can often be adjusted by moving things around in the trailer.
The position of the trailers axles also is important. The farther towards the rear of the trailer they are the better the trailer will tow, mainly because of increased tongue weight. Most travel trailer have their axles nears the middle so the tongue weight is reasonable enough to be towed by the average truck.
A Hensley hitch is quite expensive to purchase new (around $3000) but can often be found used for a lot less. I have purchased three of them. One new, and two used at less than $1000. A 5th wheel hitch that eliminates chucking will cost just about the same as a standard 5th wheel hitch plus installation and will be near the amount of a Hensley.
I would not make a purchase based on the towing characteristics of the trailer. Since a TT can tow as well as a 5th wheel at considerably less cash outlay than a 5th wheel, the decision should be based on other factors in my opinion. Until this year I have towed a travel trailer all over the country for about 17 years with a Hensley hitch with NO sway and no handling problems whatsoever. See
this post I made some time ago.
Hope this helps you a bit. :)
Barney