For me, and I'm using these only for DJing, it was an easy decision: the Beyers and the B&W headphones are both $300 vs the $200 of the Senn HD25s. The Senns have proved themselves for years by being the go-to headphone for sound engineers and djs the world over, and one of the reasons is that they are INCREDIBLY EASY TO DISASSEMBLE. Without any special tools, anyone can easily replace virtually anything on this headphone. So if you're a company buying a lot, it obviously makes much more sense to be able to repair than replace. They're also incredibly easy to mod.
Finally, this idea that plastic is cheap but metal is serious is a hangover from the 20th century. Cars are increasingly made of plastic, for god's sake. Plastic is not a single material, but a wide variety: high quality plastic is not a cheapo toy. Similarly, thin metal - as it has to be to keep from being too heavy - is not necessarily very durable, and can easily bend or break.
All that said, I'm sure the B&W and the Beyers are both fantastic sounding headphones, probably a bit better sounding than the Senns. But I would expect them to be for the price difference. And if you're really into sound above all, I'd question spending $350+ with tax and shipping for any of these cans, when there are serious models out there (senn 650s, audio-technica, etc, etc.) that have MUCH higher quality for around that price point. I've tried several DJ headphones, and they were all of so-so quality - it's hard once you're been spoiled by JH13's.
But for what they are, I think the Senns are a terrific value - even more so bc I got a refurbished pair that are like new, with a full sennheiser warranty, for only $130 (about 90 euros) including tax and shipping.