I'm been using the original Fanatec wheel for over a year mounted on a Playseat. It's a great steering wheel with a very strong force feedback motor. I also have experience with the G25 at my brother's house. Let's just say there's no comparison. I understand there's a price point difference but the G25 feels really cheap. The leather feels thin and 'dry' whereas the Fanatec has thick leather that's actual car grade steering wheel leather. No joke. The Fanatec wheel does not feel like a toy. Another benefit is that it's all wireless other than the AC plug.
I have no experience with the G27 though.