Theo's an extremely efficent player. The same way Podolski is/was. High stats, but doesn't contribute defensively at all, and is quite poor technically, but has good movement (in Theo's case) and is quick (previously Podolski was), and is a good finisher.
Sterling's the far, far, far better footballer, quick, technically gifted, good finisher and good defensively.
£20m + Theo for Sterling.