I have the Lionel GP-30 in CP and I love it! Sounds and features are great but a Williams engine is nothing to sneeze at either. I also have the Williams GG-1 Bicentennial engine which IMO they did a beautiful job on the decoration. Williams is a bullet proof engine that is fine the way it is or upgrade it to DCS or TMCC if you choose. My only long running complaint about a Williams is the sound. Not a show stopper by any means! WBB is addressing that with their new digital "non" command engines rolling out soon one of which I have a Boston and Maine F-3 set on order with the new sound package.
This is the Williams B&M and below is the Legacy diesel.