cable seems to be the most common with hydraulic a second to that. there are differences to both. Some say the hydraulic doesn't let you feel the rudder
, but holds a course better. I've never heard of a geared drive on a boat that size, it seems like it would add a lot of unneeded weight.
In my honest opinion though, why would you want to get rid of the tiller? You've got a simple system that I assume works(or could be made to work more easily than a wheel), why make it more complicated?
It's your boat, your decision, however.