It depends: distance, comfort, 2-up, mileage, etc.?
I've only owned a Burgman 650, but before I bought it, I was looking at the pre-2007 Scarabeo 500, and both Burgmans (Burgmen?) I didn't look at the Silverwing mainly because I wanted to avoid my local Honda dealer and also figured if 600 was good 650 was better. At just under 400 lbs., I'm basically riding 2-up all by myself
I sat on the Scarabeo on the dealer's floor, but didn't actually ride it. I've read that the vibration of a single is greater than that of the twin, so amount of time per day spent on the bike may be a factor. I do like the style and bags of the S500 though.
My B650 has served me very well. I bought it with just under 37000 miles on it 2 years ago, loaded with all kind of goodies. It's now at 68000 miles (I just had the belt replaced)
That's my experience and my 2 cents.
Whatever you get, enjoy!