the newer ones with solid state gyros have better course keeping - far better - than the older designs. I'm not sure there is a huge difference between the big brands unless you have something like an Open 60, then NKE seems to be ahead. The difference with the gyros and steering algorithms that use them is night and day. With my older Raymarine on my old boat (RM 6000 with a very much oversized linear drive), it would wander to and fro in difficult conditions for a few minutes, then give up and round up. Power and speed weren't the problem, it just lost its mind. The new one on the new boat (X30 and even more powerful geared drive) will confidently drive dead down wind in a big confused seaway for days at a time, never getting off course by more than 5 degrees. It steers the way you do - in response to the pitch and roll, prior to the yaw even starting. Big advances in the last decade.