Mining ore tends to bring in a lot more credits but can become boring doing the same run over and over and over...... but, being able to make anywhere from 60 to 100 million a run is pretty darn nice.
Running freight brings in less credits but still a lot... finding a commodity you can power trade is handy as well... i can make 25 million running ************* in about 15 minutes (give or take) sure you will be doing the same run over and over but meh.... what you need to do for moving freight is find a run that takes you through multiple systems so it changes things up a bit... your not seeing the same couple/few systems ALL THE TIME!
I say running goods/freight is very profitable.. as long as you know the runs.
I am currently in the process of building an "Ultimate Run". Consists of a 22 system run and my ship will never be empty, always be full and always be profitable. Going to call this run "Around the verse" (once i get it going...lots of number crunching and things to figure out.)