im thinking of booking a Bus flight with UA out of GB/Ireland and only 1 airport has Saver Award right now. If the Saver Award opens up at a better airport to my actual trip location, I would want to rebook to that one. Would it better (I saw that the price,, 57.5k miles for flight from Europe is the same as United) to book with SQ or UA in terms of tax, fees, and (theoretical) rebooking cost? TIA