Neerman is right. It is perfectly legal to file h1b without even working for the company because GC is for future employment. But normally companies won't do that. But is it legal? Yes.

I don't work for a large indian company, but from what I hear, they are alright. Its the street dhotis you have to watch for.

Generally, more reputed a company is, better the chances of getting labor and I-140 approved. So Tech Mahindra would be a better bet for filing GC.