Three considerations can help you make a good decision: 1) your body size, 2) the activity you plan and, 3) the need for accessories. The system of support is similar in all the products but there is an important difference between the effects of elastic or non-elastic support. Then there is the question of the varying extent in which pressure is distributed on the back and knees. Finally, there are accessories available to enhance the use of the products. The Back-Up is our most popular seller and the choice for those who want over twice as much cushion on the knee and back compared to other non-elastic models. We recommend it for long-term sitting tasks such as computer work and also for people (though, not exclusively) with a bigger body builds. The accessory Cush-Shins (included) distribute pressure on the upper shin over nearly three times the area making it much more comfortable for longer sitting periods. Accessory Stretch Straps (not included) engage the feet to allow hamstring stretching or long-sitting on the ground. All the non-elastic versions offer incrementally adjustable and stable positioning which is ideal for therapy or for situations where one must rely on the product for sole support, for example, at the ballgame, in a canoe or sitting yoga-style on the ground.. The S'port-Backer supports exactly like the Back-Up model but might fit smaller body builds better. What's a "smaller body build"? Roughly, anyone 130 pounds or less. Most find the slidable cushions provide adequate padding for the knees and those who don't can purchase accessory Cush-Shins. Accessory Stretch Straps can also be used with this product. The Slouch!Buster is soon to be discontinued. It provides great support but has no knee cushions - not the best choice for someone who is heavy or those sitting for long periods. Along with the BackRx, it finds its place with mountaineer or space-conscious backpacker who counts-by-the-ounce. Some rely on the elastic BackRx as their only solution. While the strong elastic satisfies much of the need for support, this product will never be the therapeutic tool that allows incremental adjustments to fully stabilize the pelvis. The elasticity provides augmented support while primarily depending on existing chair backs as offered in airlines, cars, or on the couch. Many use it as a "travel version" and leave their non-elastic model at home or work. It is also the perfect choice for those, like manicurists, dentists, assembly-line workers, who must lean forward to work and are required to frequently alter their position. It auto-adjusts according to the way you lean while constantly multiplying your muscles' effort in providing postural support. NOTE: the BackRx can safely be used for driving automatic transmission cars by simply sliding the right leg free of the elastic loop. Adequate support for the lumbar area will be maintained by the left leg. The LumbarJack knee detour LumbarJack is the only product we recommend using while driving with manual transmission. Elastic straps detour around the knees and engage the feet to allow complete flexibility and mobility of the legs for working the pedals. When you use the alternate non-elastic straps, the LumbarJack conveniently converts to comfortable sitting support using only the knees.