I have never stayed at the Anaheim Fairfield, but have passed by it. It is across the street from DL -- seems like an extremely short walk to get to the DL gate. Bonus is that you would be so close to Mimi's Cafe.
I have stayed at both the Hilton Anaheim and the Anaheim Marriott. Located on Convention Way (next to the Anaheim Convention Centre), both are about a 15-min walk to the DL gate. It is walkable, and we did it every day, but be warned that it can be a tough walk after a long day at the parks.
The Hilton is not worth the effort...the rooms are tired and weary, Motel 6 quality. Don't let the lobby dazzle you. You will be deeply disappointed when you get to your room. They are finally in the process of renovating the rooms but they have just started the reno, and given how big this convention hotel is, it's going to take a while. You may be turned off by the construction noise. Recent reviews for the Hilton have not been kind, so not much has changed since we stayed there last.
The Marriott is much nicer. We really enjoyed the hotel. No complaints.