Got to say I'd rather start Mason than either Son or Lamela. Neither of them deserves to be dropped but having that late runner just seems so crucial to our play and it's something that both Alli + Mason are good at so I think we should keep one in the team if we can.
Lamela has been subbed on 3 times this season, against United, Stoke and Sunderland. He was pretty poor in the latter two. I think he needs to start.