Reece for substrates (good prices, but truck delivery can take a toll on materials)
Fellers for printable vinyl, banner, specialty films, and inks. (Competitive pricing if you can negotiate. Really good pricing if you are great at negotiating AND order on a regular basis)
GSG only when I'm looking for oddball stuff that the above 2 companies may not have in stock (specific colors of 751 or w/e), or sometimes I need something delivered on the Tuesday delivery truck.
The biggest perk (for all of them) is free weekly delivery, or free 1-day (ground) shipping w/ Fellers Tulsa.
I used to buy from N'Glantz when they were in Tulsa, but their shipping methods/policies make it too expensive and long shipping time.
For me, the weekly delivery schedules were:
(formerly) N'Glantz Tulsa on Monday,
GSG on Tuesday,
Reece on Thursday,
Fellers every day of the week (via free shipping @ $99).
I like my current set up, and I keep in touch with all my sales reps, like showing them pictures of excellent jobs I've done related to the "better" material I was recommended by them. They are always happy to share other useful info as well. And if you want to negotiate better prices -- be the guy that has a conversation with your rep -- rather than just the "order out of the catalog through the main office" guy. Sales reps are business people too, and they can help grow your company if you let them. Treat them like a business partner and they will reciprocate. You'll get the best deals, some of the best info around, product samples, and sometimes when you get into a crunch, they'll happily drive material to you (an hour away, on the weekend, for example) for no charge. That's happened to me countless times. So yeah, I really like Tulsa Fellers, and Tulsa Reece has come through for me as well.