Actually, the stopping power of a .45 round has a lot to do with the weapon involved. In actual collections of police shootings, the .45 with a 5" barrel actually demonstrates an almost statistically perfect record of stopping power (i.e. the first shot to body mass incapacitating the subject, and preventing further threat to the officer). The same studies show in actual shootings (generally the sample is required to be of sufficient size, generally over 100 or so incidents) that in order of stopping efficiency, of the most common caliber choices, are:
1) .45 in a 5" or larger barrel configuration, 99%+
2) .357 magnum, 96%
3) .40 caliber (+P rounds) 96%
4) .45 in 4" or shorter barrel, 94%
5) .357 Sig, 94%
6) .40 caliber (standard 185 gr. rounds) 92%
7) 9mm parabellum, 92%
8) 38 special, 85%
Notice that all the most common rounds are all above 90%, and 38 Special at 85%, so they all represent a reasonable self-defense choice. Between the various choices you mentioned, the variances in documented stopping power are not sufficient to make the decision for you. They all represent fine choices, with strengths and weaknesses particular to the caliber and ballistics, mostly in terms of muzzle velocity, recoil, muzzle flash, and penetration abilities.
Rather than looking at raw stopping power data, i would advise you to find a weapon that you feel comfortable with first, and decide on a caliber second. The choice of firearm itself, in that you are comfortable using it and carrying it, is much more important than the ballistics. The best performing sidearm in the world doesn't mean much if you can't stand shooting it, and cannot come to a high level of proficiency in its use.
Personally, my overwhelming personal choice is the Sig Sauer 229, in .40 caliber, with 135 grain Cor Bon rounds. But that might be an entirely inappropriate choice for you. Ditto Russ's recommendation for the model 92 Berreta. A lot of folks will swear by Glock products, or a Browning 9mm. Do your research, carefully handle and actually shoot each weapon, and come to a conclusion first on what brand and model feels best for you. If that choice doesn't fit the normal mold of what people tell you is a "good gun," then so be it. I have a friend that swears by an old .38 Super. That's what works for him. Likewise, you should get what works for you.
Then determine what caliber and ballistics for the weapon of your choice make the most sense for you. Certain calibers might make better sense for different reasons, because of the inherent differences in the ballistics. The .357 Sig generally has much better penetration than say the 9mm, all things else being equal. That might be a plus or a minus for you, depending on your needs. Again, assess what YOUR needs are, and choose appropriately.
And no matter what your choice, or what your experience level in dealing with firearms, take a firearms safety course with your new weapon in hand. That you've been shooting a M1911 or a 12 gauge all your life, does not mean that your bright shiny new Taurus or Glock or Sig or Berreta or Ruger or whatever you purchase will function the exact way. You have to get comfortable with the action, user requirements for accurate shooting (i.e. individual variances in sighting and alignment, etc.), and safe handling of your new weapon.
Enjoy, have fun in your shopping, and take responsibility for the unique demands placed upon an owner of a firearm. Best of luck to you.