If we're picking a non-specialist right centre (i.e. Lawrence / Josh Morris), then for me Glenn Stewart is a must on that right edge. Last year all our attack cam down the left and Soward / Scott / Gasnier did next to nothing with the ball. Glenn Stewart asking questions, presumably with Carney on that side (as Pearce played left last year) with whoever plays centre and Aku Uate (who barely touched the ball in attack last series) looks far more imposing to me. And above all, balanced.
In terms of grunt work in the middle, Watmough, Gallen, Mannah and Tamou can provide that (and in a pinch so can Sims). Lewis & G Stewart provide ball-playing on the edges with some hard-running centres (I personally believe Lawrence would be a revelation outside Stewart - look at that try he scored in CvC by coming back on the angle). Then to mix it up, T Williams and Sims can come on and provide the angles on the edges from the back-row.
Farah out of dummy half with Watmough and Gallen running off him in the middle, not to mention B Stewart? On paper (and in my mind) that side has left & right balance plus some serious threat around the ruck.