Hello Mohamed
The basic rule of thumb between cargo & pax ops is that cargo is a lot more stressfull than pax. Pax will complain and work with it but cargo agents will cancel the contract and go with someone else if your company cannot fulfill its obligations to operate the route. The margins are also a lot lower with cargo than they are with pax.
If general cargo you will operate a lot of ad-hoc routes, no one day is the same. If it's a courier co like some of the well known names then it's the same old job every day with procedures set up which don't really change much apart from a major disruption like atc strikes or cloud ash problems.
Having had the pleasure to work in both kinds of operations i would say go with your gut feeling. My preference has always been smaller operators where you get do everything from Ops Control, Flight planning, Charter sales, Overflights, crew scheduling and slots. In large co's each task is given to one person and so whilst you will end up being highly experienced in whatever you choose that is all you will know.
The economy is constantly changing and so it's impossible to know which type of operation is best or indeed will be around next year.
I'm sure that many of my colleagues will have their own views and will probably differ to mine but good luck in your endeavours. Always nice to welcome new blood into the industry.