It makes a difference in integration.

Simrad (used to be known as Robertson) is, as Jim and others have said, a durable unit.
Raymarine makes a decent unit; however, if your instruments are older, the Seatalk (or whatever) may not integrate (?)

We have a B&G Hydra, hydraulic unit. It drives a separate manufacturer's heavy-duty ram (Hynautics).

The ability to integrate with apparent wind, as well as the "compase" setting is important.

If the boat balances well, and you don't push it, then a UPSIZED electro mechancal drive is usually less expensive. IF you want the power and greater reliability, then I'd go with a hydraulic drive unit. If you go with Raymarine, go one or two sizes larger. The use of the "displacement" as a measure is (in my opinion) stupid. The real issue is the controlablity and reponsiveness of the helm. Raymarine and others seem to have recommendations that are designed for boats motoring in very light seaways. Go BIGGER and be SAFER on the sizing of the loads. Even then, you have to balance the boat.

If you use the Monitor windvane as a measure, if you can trim the boat with the Monitor, you should be fine with an "Auto Pilot" which is properly sized. If you can't, then you'll be testing any Autopilot with the traditional control surfaces that you have on your beautiful Cheoy Lee.