I have an older Colt Mustang (the gun the Sig P238 is based off) and a LCP. While both are intended as pocket guns, the Ruger generally fits that role better. The Ruger is smaller, thinner and lighter making it easier to conceal; it's also half the price of the Colt or Sig (Colt is making them again).
Both guns are sensitive to limp-wristing, especially the Ruger, but in a steady hand both tend to be very reliable. You must grip the Ruger well and quite honestly, they will rotate slightly in your hand when shooting if you're not paying attention. It's not a gun you take to the range for some target shooting; while quite accurate for what it is, it's not comfortable after a couple of magazines. The sights on the latest model LCP are also improved over earlier models- though still lacking a bit when compared to the Colt and Sig (a drop of paint or nail polish definitely helps). The trigger on the Colt and Sig is single action so of course it's going to be much better than the LCP's long double action pull. The Ruger (and the Kel-Tec) should not be used with so-called +P loads due to the thin barrels; no Buffalo Bore, Double Tap, etc.
The Kel-Tec, like all of their products that I've ever seen, appears to come from the factory approximately 95% finished. You still need to do a fluff and buff and remove all of the plastic flashing, clean the magwell, etc. While most of them that I've seen went bang, I'm just not impressed.
Another option you may want to look at is the S&W Bodyguard. It's slightly larger than the LCP, but still thinner and lighter than the Colt/Sig and it has a built in laser. I've shot several of them and like them a lot also.
Personally I like the LCP as I wear shorts most of the time when I'm not working and I feel it conceals better, but any of the better brands should work well for you. Remember that any gun carried in a pocket will need to be cleaned more often as they get dust and lint in them quickly, even when carried in a closed holster such as the Desantis Nemesis.