I have a Mossberg 500 and like the tang-mounted saftey position and the position of the slide release over the Remington 870 controls. That, ultimately, was the deciding factor between the two for me.
Although the Mossberg's saftey would be great for a lefty, I'm trying to envision how well the slide release would work for a lefty (left-side of the reciever and to the rear of the trigger). I find the slide release, for me, to be very intuitive, as I just extend my middle finger and I'm able to engage it. But being a lefty...would you just bump it, upward, with the top of your trigger finger?? Guess you would have to check it out for yourself.
Anyway, My Mossberg goes bang when I pull the trigger and I havent ran into any trouble.
I have no experience with Browning or Benelli, other than reading that people like them.
As far as Winchester goes.... I never handled the SXP version, but I read it was based off of, or set-up the same as, the 1300. I have handled the 1300 and I just didnt like how the action cycles itself rearward after shooting a shell. My co-worker, who owns the 1300, absolutly loves this function. I just could'nt get used to it (granted, I didn't have much time with it).