At the top of my list is Gunrunnerjohn. He has done 5 conversions for me in the last 18 months, and there's a 6th waiting in line in his shop. His knowledge of electronics and electrical systems is seemingly unlimited. Combine that with his can-do outlook, and good things happen when you send a train to him for repair or upgrade.
When I asked John to convert my Williams Niagara to DCS, we weren't sure it would work. He emailed me to tell me what was going on, and I told him to scrap the project as it didn't seem like it was in the cards for it to work. He was determined to find a way to make it work, and he did, by making a custom flywheel tape. Combining an MTH operating system with a 30-year old loco that was made before DCS hit the market was no doubt a challenge, but he made it work. That loco is now one of the best runners I have, and a favorite of visitors.
Also, we need to posthumously recognize Marty Fitzhenry in this thread. I only knew him a short 3 or 4 years, but it didn't take long for me to learn that he could fix just about anything.
John