Apart from the inevitably non-functioning "priority luggage", I've never had any problems with Aviance ground handling. They seem reasonably competent and acceptably courteous (but it's true that they're a bit more focused when an AF supervisor is around ). And AFAIK they went as far as developing a lounge with their airline customers at BHX; this truly is something Servisair would never dream of!
On the other hand, out of my 12 last encounters with Servisair, I had problems no fewer than 11 times. The problems with Servisair seem systemic; I don't think there is a major attitude issue with their front-line staff- they often look more desperate and anxious than the customers asking them for assistance. To me, it looks like a case of consistently poor training (e.g. jetbridges) and infrastructure (lounges, IT systems).