I looked at Equitrec, laughed and moved on. They didn't even take pride in the boxes at the factory!
I looked at Alexanders, fully intending to buy, but found that, although better than Equi Trec, the manufacturing was wanting. Things such as; they couldn't tell me the weight, the floor was in pieces, wooden, with pieces of rubber screwed down on top (so water could get in, but it was not easy to inspect. There was later some legal action for floors, and I don't think they actually manufacture new ones any more. They now seem to sell new Lehel or older boxes.
I looked at Boss but, although they looked better than Alexanders, they were a bit 'lightweight' for the horse I had at the time.
Bloomfields - loved the Professional as soon as I saw it. Solid, safe, clean. Breath of fresh air.
Whichever box you go for, I would avoid a breast bar, avoid a narrow back door (the fire brigade would agree with this!) and make sure the floor/safety cage for driver are substantial. Always weigh.