I, also, agree with Stilla.
I enjoyed the TMS from my first Bible Reading (Jephthah's Daughter, at age 6) through to my DA'ing, when I had been a TMS Overseer for a few years.
Latterly I got great pleasure about helping people become good speakers, and once (with their permission) kept someone on the same point (Use of Outline) for six months, to help them get to grips with it. It had the desired effect, though at the time folks struggled to see what I was up to.
I had seen good and bad Overseers, and the effects they had on people.
Singly it's the role that I believe had the greatest effect on an individual's morale and self-confidence, and I really enjoyed seeing people blossom.