Blued and stainless guns are USUALLY made from two different types of steel (It can be hard to know today, because there are now many processes that can make a stainless gun have a dark finish, rather like some blued finishes.)
These different steels share many chracteristics, such as being equally strong and pretty equally machinable. The main FUNCTIONAL difference between the two is that stainless-steel revolvers are far more resistant to rust and staining. Stain-and-rust-RESISTANT, not stain-and-rust-PROOF. Blued guns can stay rust-free forever if they are properly maintained and not used much in very harsh environments (like in a coastal marsh, lots of salt around) ; stainless guns will not rust after pretty long periods of neglect, even in harsh environs, but they WILL rust and should be cleaned almost as much as blued guns if you want them to stay looking good.
Now, there's one other factor that comes in to play when considering whether to buy blued or stainless -- personal taste. Some folks think nothing looks better than a stainless gun; others think blue is the only color for a "real" gun. You pays your money and you takes your choice.