Cameron Starr wrote:
I have a 24' power boat I want to put auto-pilot in.

The steering is cable driven to the engine area where it is then hydrolic.

I see most autopilots for this sized boat are "cable" or "hydrolic" -- which
would I fall into?

Supplying the make, model, and year might be useful. Somebody who owns
a similar boat may have put in an autopilot, or one of the posters
experienced in that field might be more confident that they fully
understand the specific nature of your existing steering system.