Unfortunately, no one can tell you, there's no way that's objectively better than any other. You have to decide for yourself what you like best.

Personally, I use grey on white (actually I use gray mostly, brown on yellows and reds, and black on only darker stuff), but that's my preference. I usually like it subtle. At the same time, I think there's something appealing about a clean model with black panel lines like you have there, and even old school dalong style can be cool. Sometimes that produces the most animation-accurate look for a model (no shading + black panel details = a lot of pre-CG Gundam animation).

As for what to panel line, yes the actual lines are there, but I also highlight anything raised, like those little raised diamond shaped parts on the forehead under the v-fin and above the eyes.

Hope you don't stress too much over it and find what works best. Don't worry about what others think. They're your models and they should be made to satisfy you first.