Hi there
We recently did a day trip to Cartegena, loved it, such a beautiful town & well worth the visit & I would advise to go to the museums too, we did a collection of 4 which works out cheaper, a definate is the Roman Theatre.
We've stayed at the Hotel Los Habaneros before on a different occassion, we didn't dine there, but the room itself was great, nice & clean & the hotel staff were lovely. My husband has also stayed in the NH Campo Cartegena.
If you go onto Booking.com & put in Cartegena it brings up quite a few to choose from & I think that majority of them would be good enough, I think it depends on what you're looking for really, personal preferance.
Enjoy yourselves