Ruger P95 is a great gun for the money, it is bulky and hard to carry concealed. Reliable and comes complete with great customer service. I have one, it'a a good shooter.
Sigma 40 I don't have, I have one in 9mm, it has never missed a beat in several thousand rounds. Right now they have a $50.00 rebate or two free magazines by mail with the purchase of a new one. People don't care for the trigger pull, it takes some getting used to. Also, it is said that the resale value is not as good. I don't sell them after I buy them so it doesn't matter to me. I also recommend this gun, another great manufacturer.
I have only shot a Kel Tek, did not have any problems with it, seems to be a good gun for the money. It is also easy to conceal because of it's size.
As far as I'm concerned, they are all worth a look. Don't forget about a revolver in .357, they are a great gun for training, self defense, and fun.