Honda would be a tough call. I'm not at all convinced that Mclaren could effectively use a brilliant new engine, so you might get Honda being easily the best engine next year but Mclaren the only team to use it, not use it well so no one really knows it's brilliant, if you see what I mean.
Also wasn't saying RBR don't have good aero, I just don't think they automatically have better aero than Mercedes. They both look a mile beyond everyone else. But the interesting thing is, RBR are a mile ahead of Ferrari in qualifying, easily being second only to Merc, but in race Ferrari looks much closer to RBR than they do in qualifying. You would think to some degree if RBR had the engine/aero combination to be faster in qualifying and Ferrari are another second back from them, the aero/engine combination wouldn't be bad in race either.
I think that points to a relatively good engine in max power output, both fuel and electrical, but over a race distance the efficiency isn't good enough to sustain that level of power usage.
It's better than not having that max power achievable at all, it's less things to fix on the engine. As you say, can't see Merc giving them the same engine, nor Ferrari, which leaves renault or Honda. Stick with Renault and hope for better or pray Honda get it spot on straight away, think Honda are a bigger risk.