In my opinion right now that the best way to make money in the short term is thru mining, but what about longer term? At what level (with UEC available) does it become more profitable to run cargo around the verse instead?
25,000 to 40,000 in hand? Opinions?
Cargo is tough. I have lost a lot due to disconnects and bugs. With the new aUEC in place I am able to play by being financially independent. 
4Fun, do you mean in the alpha, or when the PU goes live? Those are 2 completely different questions because any money you make now will be wiped multiple times before “launch” and bugs will always be the biggest factor to contend with.
Once you can load about 30k of cargo it is far better to run that than to spend time mining.
Best case average mining profit is about 2k per hour. You can do better but that is about the average.
Once you can run cargo in excess of 30k you can make more than that in profits easily.
The catch is to be sure that you have at least 60k saved up before you load 30k in cargo. Always have that buffer because pirates are out there in force these days. And crashes and bugs will steal your cargo as fast as any pirate too.