Best FBOs as far as I'm concerned:
Mercury Air Center ... every one I've been to (ATL, PDK, CHS, BNA) has been terrific.
Wilson Air Center (MEM) ... that canopy is great when arriving in the rain, and they have a super reduced rate at the Peabody ... about $140 as I recall.
Say what you want about Signature ... but their EWR and CLT facilities have taken good care of me on more than one occasion.
FBO AvCenter at SDF and PIT ... fuel is expensive, but the facilities are nice and the people are very helpful.
A few others that I've enjoyed:
TacAir (LEX, BDL)
Banyan (FXE)
Yelvington Jet (DAB)
Galaxy (PBI)
Million Air (PWA)
Regal (DAL)
R