What about a used ithaca model 37.
Granted, it doesn't have a tang safety, but it throws em downwards, and any gunsmith should be able to switch the safety to left handed.
This may sound odd, but several years ago, i had to make the same decision you did (although it was more a hunting gun than a trap/skeet, but it was a general all-purpose gun. ) I looked at bps, wingmaster, rem 870, and ithaca 37.
I wound up with an 11-87 lh.
Browning seriously downgraded thier bps line sereral years ago. If you realy want a bps, look for a used one made sometime in the 90's. It should have nice scrolled engraving on it, and it'll probably have a decent stock.