I don't have any experience with these petrol engines but our flying site might be slightly noise sensitive. For both the MVVS 45cc and the MVVS 58cc, what would be the quietest exhaust system for it? I was thinking of the wrap around system. I would like it to be light as well.

Use the canister system for both. Quiet and you don't loose any power.

I use a Bisson wrap around muffler on my MVVS 58 and it is not quiet.