In late ’57 or early ’58, Braniff International Airways was the first American based airline to order and take delivery on the B707-100 (the smaller water-injected engines).  I remember the black smoke boiling out of the extremely LOUD JT3C engines on take-off at Dallas Love Field (KDAL).
My father was 37yrs with Braniff and he saw the growth of the airline from the Lockheed Electra (2 engine tail dragger), DC-3, DC-6, DC-7, Constellation, and finally the Jet –Age with the Lockheed Electra TurboProp and then Jets.

I think I remember, on a “Fairy Flight” about 1960 – 1962 (only Braniff employees and family were allowed to fly these asset repositioning flights) from KDAL to KMIA, I had the opportunity to sit in the right seat of a B707-100 on approach into Miami before the Co-Pilot took over.

I would VOTE for the expansion models: B707-100 or B707-227 with the Braniff El Dorado paint scheme.

Note: “The -200 series was made for Braniff who required a 'hot and high' variant to use in Latin America. Very similar to the -100 with only five examples made, the main change was the JT4A turbojets”.