Avoid anything low powered or with dubious handling - which is typical of older style scooters. I have never ridden one of the whizbang 600 cc scooters now available, as they don't appeal. A motorbike needs a few essentials such as enough power and good handling to get away from that tailgating B double/tosser in his boy racer, anti lock brakes, some weather protection (no such thing as complete weather protection) and dry stowage for your overnight kit. If you are doing big distances you won't want the clip-on racing handle bar style, even though they can look rather cool.
Buy the best you can afford, which does not mean the biggest. Big touring cruisers with a rear armchair and stereo for the wife/current squeeze are not suitable for a daily commute. If you can't pick it up after you drop it in the car park, it is too big (not to mention you will look an even bigger tool).
But if you drop it at speed, picking it up is academic.