In 12 years of GTR ownership, (My R33 GTR) I think I have tried about everybody out there, new and long established. All I can say from my own experience is that different "tuners" / “engine builders” have different skills!
I had my engine built by one, my tuning done by another and the car set up for the track by another. It’s a bit like trying to find the car with and that does everything you want, it doesn’t exist so you have to compromise and each and every experience is a learning curve as something for one might not be something for another. Also, a lot depends on customer service and personal interaction. I know of some who have appalling customer service skills but can built a bloody great engine!!!!