Welcome to the forum nikkusunitha! If you read around a bit you will note that our Independent Contractor Agreements (ICAs) do not allow us to disclose who shops whom (with only one exception that I am aware of and they have only one shop that is not any of the ones you name). Similarly the posting guidelines for this board indicate "Do not reveal the clients of mystery shopping companies."
"Good" mystery shopping companies vary by personal experience, expectations, geographic location and other factors. I can recommend to you that you first sign up with companies that have nationwide clients so you are more likely to quickly have access to jobs to try them out. These are reliable companies to get started but in the long run have fairly low pay structures. So sign up with Market Force (blue portal), Bare, Maritz and Corporate Research International. These companies also will offer pretty decent instructions to get you started.