We arrived a day early and stayed at the Marriott Courtyard next to the Multiplaza Mall. I highly recommend this location for a hotel. The mall is high-end and has restaurants. We used www.myfriendmario.com for transportation from the airport to the hotel ($12.50 per person). They also transported us to the port for $23/person. They were early and professional. It took 1 hour and a 1/2 to get to hotel from airport. It took 2 hours to get from hotel to port.
In Cartagena we walked outside of the port to get a cab to the Old City. When we negotiated the rate we thought we were talking to the cab drivers. We were NOT. The people we talked to were tour guides who charge you a tour fee plus the cab fee. You need to make sure you are talking directly to the cab driver and it should be $10 to the old city. Inside the port it was $20.
In Aruba, we walked to the bus station which is outside of the port and to the right. Take bus #10 to the hotel/beach area. $2.30 per person round trip.