Probably a wise choice. The only mod I have made on my 870 (factory 20" barrel with rifle sights installed) is a sidesaddle for six spare rounds...
Nice gun, being a lefty, I like a Ithaca 37 with a 20" rifle sited deep barrel
According to what is most important to the lefty (safety catch or ejection port) either the Mossberg (safety on center of receiver) or Ithica (bottom ejection). I used to get left hand safeties on all my Remingtons, but then realized when loaning one to a right hander it made for confusion. I just adjusted to right hand safety.
Of course we have glossed completely over the Benelli (sp?) line of shot guns. Kinda high dollar compared to an 870 express though.