I can only talk about the sig and the 99.
I have had both for 3 years or so, and have put about 3k through the sig (40cal). and about 1k through the Walther (9mm), reloads and factory. I am very happy with both guns, and wouldn't sell them if I needed money (isn't that the best endorsement one can give on a board with an efficient EE!).
Out of 4k rounds, i have had only a handful of malfunctions with either gun. I'm pretty sure the sig was because of a bad mag, got rid of the mag and it has run perfect since. I'm not sure what the deal was with the Walther, but all malfunctions with it were in the first 300 rounds, so ill chalk it up to break in issues. I don't like the trigger that much on the Walther, but its not a 1911 so its expected and no worse than a glock and its better than a ruger or SW auto. The sig is much like my full size, non plastic sigs, only the pro gets carried a lot more when I am out because it is just as reliable, shots the same, but I spent much less on it so i don't care as much if it gets stolen or taken by the cops if I have to use it. The Walther is just a fun gun to have in the safe. Some folks on the first page said that the pro has a rep for reliability issues, this is news to me, and I have not had any more problems with it than any of my other guns.
They only thing I have bad to say is that at one point I had the full size sw99 in 45, and I didn't care much for it and its reliability issues, so i sold it. Its smaller Walther cousin has been much better.