The 55-200 may be more convenient but when lens makers design a lens with such a wide range...they have to make compromises and the image quality suffers. Typically you will find the best image quality for the price come from prime lenses that do not zoom at all.
Also, each lens has a maximum aperture. That is the adjustable (in most cases) hole in the lens that lets light though. The bigger the aperture, the more light can get though. But to make the aperture bigger, the lens has to be made bigger with more glass etc. The maximum aperture is also listed in the name of a lens. For example, you can buy a 70-200 F4. (70-200 being the 'zoom' range and F4 being the biggest aperture) (smaller F numbers mean bigger aperture). Or you could buy a 70-200 F2.8. The F2.8 version will be twice as expensive because it has a bigger aperture and is therefore a bigger lens.
Most zoom lenses will have a range of maximum aperture. For example the 55-200 is [f/4-5.6] This means that when you are at 55mm, the maximum aperture is F4 but when zoomed out to 200 the maximum aperture is only F5.6
Also, some lenses are just better than others. There are many different ways to measure the quality of a lens...it can often be hard to figure out which one is best. Typically, the best way to quickly measure quality is to look at the price. You get what you pay for and better lenses cost more money. That being said...the words Canon & Nikon on a lens will often mean it's more expensive. Brands like Sigma and Tamron may sometimes be more economical...although the best lenses for these cameras will probably come from Nikon or Canon.
Do some reading. Look up things like Aperture, shutter speed, exposure etc. Once you have a better understanding of photography...picking a lens will become easier.
