Our view: it comes down to temperament
Both routes can work, and many great comfort advisors started as techs. A tech who sells well is curious about people, comfortable talking money and doesn't mind hearing no. A tech who mainly knows the equipment tends to explain the system instead of helping the homeowner decide.
Our advice: promote a tech who is already turning service calls into sales. Otherwise, hire a proven seller and let your techs keep feeding them good leads. Your best techs stay on the board, and your leads get a closer.