Airports always have less corruption etc. Think of the hundreds/thousands of years the ports have had to perfect corruption! Airports HAVE TO work quickly and efficiently, and thus have less hassle. Not to say there won't be some problems, even if it's not corrupt, there will always be some and it will always vary.
As a general rule, airports are better - less hassle, less corrupt, and much cheaper to get stuff out.
Agents - have you had a look at the Shipping Database to see what others experience has been? Link in the main menu left, under planning.
Seek, and ye shall find.
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