I'd say almost any approach may be appreciated, but it may have more of an impact on you than that person. It just really depends on the vibe of the company.

I'd say almost any approach may be appreciated, but it may have more of an impact on you than that person. It just really depends on the vibe of the company. Years ago, I'd done phone calls to companies, asking for a manager (shift, dept, store, regional, whatever), and almost always they were... somewhat agitated/defensive. I expect 99% of phone calls they get were people calling to complain. I'd say something like "I dealt with person XYZ the other day and... they were phenomenal. This was some of the best service/care/etc I've had. You keep that person and/or get more people like them and you've got a customer for life". That sort of thing. In one case, the person said "ok, thanks." and that was it. In most other cases the person was generally pleasantly surprised to hear good news. Looking back, I'm pretty sure a written letter or email would possibly have done more 'good' for the person in some respects, but having a pleasant/positive conversation with someone talking up good points about another person was, for me, a positive experience in itself.