I'm going to join the crowd and say ForScore. In my years of gigging I have used it consistently, and I don't think I've EVER seen an iPad user playing from a different app.
My go to for scanning music is NOT to use my phone or iPad as the files are usually huge and can slow program down when you amass thousands of scores. I scan everything from the Xerox or Ricoh copy machine at school and email it to myself. When I open the email on my iPad, I click share the file and open it in Forscore. A 15-20 page score is usually like 750kb vs. 5-6Mb if I scan with my phone.