Cartagena or Santa Marta for work and living?

I think Santa Marta is the easy winner. The beaches in the area are better, and there are just more places within short distance to explore and play from Santa Marta.

I think the first question is do you have the legal right to work in either country.

Cartagena probably offers more possibility of finding work as a non-Colombian. Although the beaches in CTG are not as attractive as those near Santa Marta, it's easy to get to the islands if you want so spend time on a beach.

As fluffy_bunny notes - you will need a work permit.

I second the Santa Marta vote. It's a pretty interesting area, and the cost of living is cheaper. However, as noted above, you'll find more work in Cartagena.

Generally speaking you will need a work permit, but this is Colombia, and there are ways around things like permits. Getting an English teaching gig sans permit is pretty easy. A lot of the smaller operations pay cash and many don't care about work permits. I did quite a bit of work in Colombia before I obtained my visa. Some of the bigger institutes in the bigger cities do offer work permits, but I don't know about Santa Marta or Cartagena.

How did you get your visa?

@south_londoner - It was pretty easy. I just went with the GF to a notaria and we got permanent partner status. After the notaria, we just went with all the paperwork and necessary documents to the office in Bogota, paid the fees, had the interview with the agent, and left a couple of hours later. It's a pretty easy process as long as you have everything in order.

Airbn;
I suppose you have a Colombian girlfriend? Is a high level of Spanish required (for instance for the interview)?

Monica,

Yes, she was my girlfriend at the time (she's now my wife). The interview process was surprisingly easy, and our interviewer spoke English as well. I had heard different stories in regards to the interview process, and i was under the impression that they would interview us separately to make sure our stories matched. However, he just asked us a few basic questions (where did you meet, work, etc), and we were never separated. I got the impression that it's a pretty easy process if you have your documents in order and can pay the fees. A year later, when I got my visa renewed, the interviewer didn't ask us anything. The hardest part of the whole process, was finding a competent notaria. Unsurprisingly, most of the ones we asked didn't know the regulations. We finally found one in Parque Poblado (Medellin), and the process was pretty easy after that.

Muchas gracias!!
Haha, in that case I only need a Colombian boyfriend :).
What about solo persons? Do you have any idea? Which country do you come from originally?
I'm thinking a long time about teaching English in Colombia :)