Yes I have taken an upgrade exam? My suggestion would be to go with the Upgrade.
In terms of: -
1. Level of difficulty
Comparatively the level of difficulty is lower in the Upgrade exam but not much lower.
2. Preparation
Preparation should be very simliar between the two exams. But you should already know most of the stuff.
3. Any advantage each one has over the other?
Fewer Questions and lower cost
Cheers!~