Scooterotica

I've an LI150 S3 bored to 175, im wanting to upgrade but not sure whether to just change the engine to a 200 or go along the lines of the Imola or RB20 !!!!

well its what can you afford ,what it going to be used for ,rb new kid on block and might be top of price range,imola tried and tested,or the 200 engine once checked over can be very reliable motor

As Tosh says. It's what you can afford & what you're after. I've got an Imola and think it's a cracking little engine and does me fine. Don't know anyone with RB yet to compare.

There's no definitive answer, it's down to cost and riding style as Tosh says.
For most a Mugello 186, MEC race crank, new bearings an seals, 22mm carb and 42mm AF clubman. It'll out perform a std 200 and the most over looked part is that it won't need 1,000 miles to run it in. With a new 200 lump I'd still change / uprate the crank and change the bearings and seals.
It's the perfect set up for 80% of the scooterists I know, it'll cruise at 55 to 60 and touch 70 depending on gearing and still do 70 mpg. Then there's the 10% who are happy trundling around and doing Alliance rideouts at 40mph and I'm in the last 10% that like to twist the throttle a bit more, so it's RB for me.