a 125cc 2-stroke vs a 650cc v-twin...for a road bike? uhhhh, i'm going with the 650cc v-twin. the aprilia is just a glorified pit-bike...for goofing around on...plus, i'll bet it's expensive as hell.
the 650cc v-twin in the sv produces smooth, tractable power...great first road bike, that would give you years of dependable service.