Which is better?
Well, try for yourself. Most shops set out samples so you can taste test the multiple varieties. There are original, chocolate, banana, and coconut flavors from each brand. Then each brand also has one ot two unique flavors. It is possible to buy a sampler pack that has 6 small rum cakes of various flavors.
Tortuga Rum Cakes tend to be a bit more expensive and are more widely distributed. Several cruise lines sell Tortuga Rum cakes onboard.
In September 2004 Cayman was heavily damaged by a category 5 hurricane. Tortuga Rum Cake Company used their Miami warehouse and their expertise in international shipping to facility staging and transport of relief and rebuilding supplies. Their good corporate citizenship won a lot of respect in the local community.
Blackbeards, as a smaller company, just didn't have the resources in place to do such a thing at that time, but they are a well regarded company in their own right.
BTW, did you know that Rum Cakes are the #1 export good of the Cayman Islands?