slide outs, different kinds?

Texas on the road wrote:
I have seen 3 types of slide outs on travel trailers:
1. Cable on the side of the slide out.
2. Tracks on the side (one up & one lower)of the slide out.
3. Beams under the slide out, (nothing on the side)
On whatever travel trailer you are looking at the salesman always says that is the best kind.
Can anyone advise what the differences are, and which is the most preferred & trouble free.
Personal opinions are welcome.
Thanks.

A forth kind is the one I have made by LIFTCO and is completely supported by the frame that is installed in the wall and has no physical attachment to the trailer except for the metal frame installed in the wall. It float over the floor and is operated by two "screws" run by an electric motor. It is not subject to sagging, etc.and has external supports on each corner that are anchored to the wall frame.

Larry