Client-side or supply-side? It seems such a simple question, but in practice the response is much more complicated.
Consulting firms can be notionally divided into those that offer independent advice and those which have obvious ties, perhaps to a specific vendor if they’re an IT consultancy or to a parent company in the case of the consulting arm of an outsourcing company. In theory “tied” firms have a vested interest in selling the services of their partners or parents and therefore cannot be trusted to act in their clients’ best interests.
But this logic falls over in several ways.