Re: Who's side are you on?
DoFP has at least a dozen characters that will be more important than QS. Singer just wants him for an action sequence. i doubt he gets more than 5 mins in that movie. Whedon however, has an actual arc for the Maximoffs in his movie. If i had to take sides, i would definitely be on Marvels.
There are many mutants with superspeed that Singer could use if he just wanted that ability. I can name 3 off the top of my head. I don't see why it has to be Quicksilver at all costs.