Depends on what product your looking for from each.
Loeffler-They have good var, and the Ref-b is pretty good also
Denkall-All products are good, but I wouldnt do the T400
Jurox-I think they have some good test suspension.
Aratest-Never used em, but I would use Denakall, Quality vet, or Loeffler, over them.
Like terminator said they are all vet companies so its not as good as human gear, but some people like it. i have used Vet gear with good results.
If your gonna do vet gear I would try and get Quality Vet, over the rest, except the Anavar which I would use Denakall, or Loeffler.
Hope this helps, welcome to the board, keep asking questions, and then ask some more, and you will learn quickly. Mrpg13