Crucial is owned by Micron and Micron is one of the best manufacturers. So when you buy Crucial you always get Micron made modules. With Corsair and GSkill you never know who the manufacturer is even with the same model numbers. You might get Micron, Hynex, Elpida, Powerchip even Samsung.
Corsair and GSkill use high end modules, don't get me wrong but with Crucial you know exacty what you are getting.
Here is a very incomplete list of modules by part number from different manufacturers if you are interested. It's the best list I have ever found though.