I've bought a few things from SparkFun over the years, not common components for sure ( for basic parts is hard to beat http://www.taydaelectronics.com/ on price). What I do like about SparkFun is their user reviews and comments on most all their products and their publishing of links to schematics, datasheets, arduino software libraries to support specific offerings. AdaFruit is also another company that goes out of their way to add support stuff to their offerings. So maybe that has something to do with the following and sales that some arduino distributes have over others? Price alone is not always what closes a sale. 
Lefty