Brand is left to the owner, if you turn to page 38 in your manual you will see a chart, you should select the best oil, Kymco calls for SAE 15W-40, but you can get from 5W-50 to 20w-40, 20 W-50 and this depends of the temperature or the region you live in,also is the viscosity what is important, no so much the brand.
Also I heard from people not to use synthetic oil during first 1000 miles, after that switch to synthetic oil, hope it helps.