Stainless guns are less prone to rust in humid environments. Some people feel stainless guns stand out more tactically... bling. IMO I think there is something to that but don't give it much value if at all. You can get blued stainless guns... but it does not look the same as traditional bluing.
All my guns are blued, not necessarily by choice. I wish on at least one I would have got stainless... because I live in a damp environment. I've owned my guns for years... they have been exposed to heavy condensation mostly from the cold outdoors. Hot, cold, hot, cold, a little bit of rain... the bluing is wearing, the edges are naturally dehorning.... there is no rust, I take care of them but once the bluing wears off it will rust there after exposure quickly and you must take care of it. I should re-blue mine soon. They shoot as good as anything new and will last a lifetime...
lightweight, cheap, strong... pick 2