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.
1. S&W Sigma 40 cal. takes a little getting use to, but the best of the three.
2. A smell their breath gun only. KT.32. I carry a KT-3AT all the time.
3. Never cared much for the P-series by Ruger. JMHO.
I expect this is your first pistol as these are three truly different pistols in different calibers, pistols size.
The Ruger P95 9mm is a good pistol and for the money might be your best choice.
The S&W Sigma40 is 40 cal more snap/recoil and in MHO not the best of S&W
The KelTec P32 is a small pistol with a small 32 acp round.
I have shot all three and own three of the Ruger P series (P93 in 9mm, P94 in S&W 40 and P95 in 9mm). They are solid pistols that I enjoy shooting all the same I prefer a S&W just not the Sigma. If you want a S&W look at the M&P, it's more money but holds it value. Same can be said for the Ruger P series. the other two pistols on your list don't hold there value. The KelTec P32 at best is a good back up pistol but not something most would use for a first line of defense.
Best to find a range that rents and shoot as many as possible then make your choice.
Good luck and let us know what you decide to purchase.
Apples & oranges. A Kel Tec .32 and either of the others are night and day. You can't shoot a KT accurately past 10-15 yds and you can't put a P-95 in your sock.
All you're going to see are personal opinions. Shoot them all and form your own.
I think the Ruger is a block but the best choice as far as value and reliability is concerned.
I am not a fan of the Sigma line but love the M&P pistols.
The Kel-tec is a pocket pistol that you could carry every day. Its a close up and personal weapon. I have found that they are particular with the ammo you use, they can be fussy, so you have to find the ammo that will cycle reliably.