Yep, you're probing into territory here that is somewhat subjective. Clothing is a form of personal expression so, ultimately, express yourself!! Most of us live and work in environments where, if we were to be too concerned about clothing norms, we wouldn't be wearing kilts at all.
Having said that, I'll follow the example of others and offer an opinion which is just that, AN OPINION:

Tartan kilts are extraordinarily beautiful garments that should be the focal point of an outfit, with the other elements working to complement but never distract from them. I think a contrasting waistcoat could do that, but if you choose one that is a strong statement in an of itself, you're probably going to distract a bit from your kilt.

I think your first choice would distract. Your second would be less distracting, although I would be concerned that the notched lapel of the waistcoast would "jangle" a bit with the lapels of the Argyll jacket you plan to pair it with. END of OPINION

Most importantly, have fun putting together your kit and make sure you love the choices you make and don't just make a choice based on what everyone else thinks.

:ootd: