There are some good places out there - there are a couple of things to consider here - especially since you say service counts too.
I have been involved in this hobby for many moons, and I have gotten parts from a lot of different vendors. I have seen a lot of rants about CJ's, MU, NPD, etc., some justified, some maybe not.
I can tell you that day in and day out Virginia Classic Mustangs has the best prices and great/arguably the best customer service. The only complaint I have heard about their customer service is that sometimes their phone is busy when trying to place an order. You can check out their website here -
Home Page
Also for certain parts (Pertronix, humphugger consoles) I go to Ponderosa Mustang - Matt is a super guy and has the best prices on Pertronix ignitor systems and components.
PonderosaMustang.com
Suspension - OEM type stuff anyway - Opentracker Racing Products
Opentracker Racing Products John knows his stuff and is great to deal with.
And - if I need some stuff fast (next day) I use Mustangs Unlimited (in Georgia) - but I usually call one of the sales guys on their extension and get them to process the order to make sure it goes out that day and that the item is in stock. I usually get the item the next day.
Mustangs Unlimited - The Premier Source for Mustang, Shelby and Cougar Parts and Accessories
I have gotten a few deals from CJ's off their ebay store, but you have to be careful - sometimes their auction prices are more than the regular price.
If you have to have body sheetmetal shipped, I have used Doc's Mustang when they have their annual sheet metal sale
Doc's Classic Mustang Parts for the 1964-1973 Ford Mustangs. but I usually prefer to pick it up from a store within an hour or two or three drive because the shipping is so much and the shippers tend to damage the parts.
NPD has some stuff you can't find other places,but I do not like the inconvenience of having to email and order in and get a quote two days later with prices that are usually higher than what was in the catalog. You end up wasting three or four days to get an order processed. (not really a slam against their customer service, just the way they do it, and their products are good)
My $.02