For my airlineapps and pilotcredentials accounts, I used a mix of internal and external recs. For UAL, I used all internals because I know lots of people there. For DAL and AA I used both internals and externals because I don't have as many contacts there. I also got a couple of hard copy letters from former CCs that I attached to the three pilotcredentials accounts along with my resume. I know that SWA will ask for internal recs after the interview invite. As with most things related to airline interview selection and hiring, the "right" thing to do seems to be difficult to suss out.