Trigger smoothness and weight are vital considerations. I'd opt for the Springfield XD if you like the look and feel of it. I've heard nothing but good things about it. I don't know why Smith & Wesson goes through the aggravation of getting a good reputation for its autoloaders, then squanders it on the Sigma series. Their first forays into autos was the Model 39/59, which had a dreadful reputation. They finally fixed the problem and came out with a great line of second and third generation pistols, only to piddle their reputations away with the Sigmas. The M&Ps have a good reputation, but I don't think they're number one in their class.
A Ruger Mark II/III pistol is an excellent investment. Ruger's autos are reliable, but are a bit clunky, but they have a sizable following.
I don't like aluminum frame guns at all because they just don't hold up to sustained shooting, but the polymers seem to be holding up okay. I love my stainless steel S&W 5906, but if I had to carry it, I'd probably need some of those helium balloons to tie to it so as to lighten it. Still, it will shoot into the next century.
As far as shooting guns, you may eventually want to try a revolver. After awhile, picking up brass becomes a pain and the loads, in autos, always seem very similar. But with revolvers, you can go from stiff loads to mild loads, defensive loads to hunting loads. If I were going out camping and hiking, I'd pick a good .357 mag. revolver. There are many, many people who consider that their favorite caliber because of its versatility.