What Name to put on application

I've been networking with a lot of bankers over the past few months and as I'm starting to apply and on the application it says to put my legal name but I have been using my nickname for the longest time and telling bankers that name. There's a preferred name section where I put the name I use most but when bankers look at my application will they see my legal name or my nickname so they can try to push my resume through.