Dr kit is nice, many people swear buy them. My uncle had one and on his Grande for a long time, definetly lastly cylinder. The transfers are pretty big for a Vespa, you will want to case match.
I have always liked the malossi, super nice quality. Probably not as fast as the dr, but you can slap them on a bike without case matching even though you should.
The old 43mm Polini is sort of garbage, maybe the new race one is better. Super weak exhaust flange.
Polini variator is the best, with a mild setup you wouldn't ever have an issue with a malossi though.
Any of those pipes. Proms is my least favorite, but they are not bad.