Harold57 has it right. There is a lot you can predict/estimate about the performance by looking up the specs. Unless the vendor advertises the actual chip(s) and lumens output for their product, it will be hard to know what you are really getting.
When LEDs are manufactured they are ranked according to their brightness. They are categorized into "bins" or "groups" that are designated by letters and numbers. The higher the letter, the more efficient the product. The more efficient (more light per unit power), the more expensive the product. The manufactures are striving to increase efficiency and you'll see higher rankings become available as their manufacturing techniques evolve or they start up a new product line.
From what I can tell, the items with the single LED are based on the CREE XLamp XP series.
a data sheet is here: http://www.led-tech.de/produkt-pdf/cree/XLampXP_B&L.pdf
If you look on page 3 you can see a table of the outputs for the various group codes. The "Q5" and "R5" are currently available in the 7440 packaging used in our backup lights. As you can see they have minimum outputs of 107 and 139 lumen for the conditions tested. This is about 30% brighter for the same power.
Usually the light pattern or beam size is also listed in specs for LEDs and is based on how the LED is packaged. Most LED chip are encased inside a plastic or epoxy package that has a lens molded into it. The lens shape determines the pattern/beam size. Many of the newer high power LEDs do not come with a lens. It is added on by the manufacturer of the end product. Regardless of who provides the lens, the physics are the same. Given the same emitter, the lens can spread the light into a smaller (brighter) pattern or into a larger spot that will not appear to be as bright (even though the total light is the same).
Also note that another wild card is that you vehicle's lens also acts to spread out the light. The original light bulbs are not directional. The light housing is designed to reflect the light from the bulb out the front of the lens. That is why there are coatings on the backside of the housings are reflective and the inside surfaces of the lenses are shaped the way they are.
So if you want the most light, look at the total lumens and the products that have extra LEDs pointed in funny directions (other than straight at the vehicle lens), as they will likely be brighter and perform better. Just total up the lumens and it will give you a feel for the differences.
This is only part of the story because the actual power throughput is based on the current running through the LEDs and the color of the light. In general for these simple circuits, higher vehicle voltage means more current through the LED and a brighter light. The LED bulb’s internal circuitry is the other wildcard and is based on the vendors design. Another thing to consider and play with is the color of the light and to optimize it based on what is using it (cameras and human eyes). Color is also a personal preference. I like the whitest whites and others look at what I like and see too much blue in it (a “white LED” is a blue LED that has yellow colored phosphor on top of it. The phosphor emits the white light).
Like everything else, find what is good for you. It’s just that with this emerging technology, it can get expensive to play around with these things and it is guaranteed that they will continue to get better. Whatever you buy today will be “obsolete” or not nearly as good as what will be available real soon.