PCI

We are currently looking at various vendors to have a PCI review done.  We have contacted a few vendor for proposals and have found the vendors are not in agreement with what type of compliance review we are required to have.  I'm wondering if anyone else has had a PCI exam or audit done, and if it was done by a qualified security assessor.  If so, can you tell me who you used for this service, if you were required to have it done by a QSA and how they defined your organization (service provider, merchant, etc.) and why? 

Any help would be appreciated.