"To work with ____" means you have an equal status to the company. If you go there to work, then you say "work at ____". Your third option is "work for ____", which means you are an employee ("at" can include freelance workers, under contract).

Both of them would work. But if you want to be technical about it "with" implies that there is some kind of partnership involved.

Both are used, both can be used successfully, but they tell a different story about working there. These are two of the small common words which is in the book "keys to words", each meaning is completely illustrated. Find the book at: http://www.keys2words.info/ My Skype: brian.madden4