information from http://www.mobility-advisor.com/transport-wheelchair.html
three major factors to take into consideration.
Chair Weight: These chairs are usually made from lightweight aluminum or steel tubing. Make sure the chair you select is easy to lift, fold and move into and out of vehicles.
Comfort: Transport wheel chairs are not designed for all-day use. Even so, it is important to find one that is comfortable. The most common seat width is 19 inches; though, many models are available in 22 and 24 inch seat widths. A cushion or pad can be used to make the chair more comfortable.
Maximum Carry Weight: Many heavy-duty models have the ability to support up to 250 pounds. Always check weight capacity before making your purchase.