The vision jet and the VIP charter missions are great, the money isnt bad either although you do make more on medium cargo. The vision jet is such a good aircraft, and once you've figured out how to use the aircrafts instruments to program landing vectors for ANY runway, it's basically like every destintion having an ILS/RNAV system, its just a dream to fly and it handles any weather.
Only problem is there is a bug in the game since new years day (literally like the millenium bug) that means that most of the missions in certain categories have dissapeared, including VIP charter missions, so you may want to keep an eye on that because until they fix it, you aint doing jack **** in your vision jet.
At the risk of giving you spoilers, if you do go medium cargo get the pilatus PC-12 is a MUCH better plane than the Cessna Grand Caravan, its not that much more expensive either.
The PC-12 is another fantastic aircraft, its what I am flying now and I've more of less figured out all of the navigation system, although using auto throttle through the FMS is a bit glitchy. The Cessna Grand Caravan is a piece of junk, it will kill you sooner or later.