I used to own a Panel Shop, these are my experiences:
Hammond; Good quality, difficult company to work with. They are Canadian and if you are in Canada, they are great but if you are in the US, they apparently couldn't care less if you get what you want and get it on time. Pity, but that's my experience as well as that of my rep at the time. He eventually gave up the product line out of frustration.
SCE (the ones in the Factorymation link); Quality is as good as Hoffman in my opinion, and they are great to work with, very responsive, good customer service etc. Made up of ex-Hoffman employees by the way. Buying from an on-line source like Factorymation though will separate you from that to some extent. I would suggest finding a local distributor.
B-Line (Cooper); Poor. The joints are sloppy, the hinges rust and the doors don't line up, meaning they will leak. Maybe they got their act together in the last 5 years, but my last experience with them was my absolute last. I will never give them another chance. Their target market is construction contractors who need an occasional industrial enclosure.
Wiegmann/Hubbell (as sold by Automation Direct); Also poor, on par with B-Line, but add to that a bad painting process. When you punch a hole, the paint blisters around the punch site and your pilot device ends up holding the paint on.
Other notable good ones:
Rittal makes a good product, but not the typical "gray box" style you may be used to.
Bel makes a very good product, but again, Canadians and in their case, FRENCH Canadians! My company sells them and the quality is very good, but thank goodness we maintain their west coast warehouse for them, otherwise the delivery would suck. Their website is also difficult to navigate.
Others worth mentioning but not worth bothering with in my opinion:
Eurobex (now called EXM?); poor quality and delivery.
Gaylord; another small mfr who caters to the construction trade but has NEMA boxes.
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