I have two bikes; the S40 and an old XS 1100
comfort, especially on longer rides, XS wins hands down
handling, XS also wins (sorry guys, a well balanced riding position gives me the confidence to USE the bikes cornering ability, and less rake = quicker steering)
I prefer the S40 due to engine vibes (I find a single sounds / feels more relaxed, for me personally) and the ease of parking lot maneuvers (the XS is TALL and HEAVY, making it hard to back on uneven surfaces)
If I hadda have one, though, especially if it also had to be my main transport, it's be the XS
however, if the seat is your only gripe, fix it
if I had just the S40, I'd likely think about the CS2 kit
on th other hand, for that money, I could get a nighthawk
otoh, I still like a single better