Why don't you test drive both? the 300i is a nice scooter, powerful and slim, not sure how it would handle in long distance trips. The Xciting 500 is designed for long distance trip and it has a powerful 500 cc engine. Like someone said choose the best for your riding style, but if you planing to do some touring the 500 is your number.
On a personal note If i had taken a look at the 300 I would probably go that way instead of the super 8, just because the 300 can get me farther out, but still is not really a touring scooter like the 500.