When I look at boats with hydraulic steering, sometimes the cylinders are mounted between the drives and sometimes they are monted to the outside of the drives. It would seem to me to be stronger on the outside but I don't know. Is there a preference (besides personal) for mounting the steering cylinders? Pro's/Con's???

Almost always dictated by space, inside and outside, on where to mount them.

Space and personal preference would be the only criterias.

They are a stronger set-up on the outside. But, in most cases, it is a packaging issue of where you can fit the rams. On a twin engine boat, it is a little easier to plumb with the rams in the middle. But, access can be a real pain on a retrofit.