Fishwiz4. You have officially entered into one of the greatest and long running debates in firearms history, the 9mm vs. .45.
There are two basic schools of thought in regards to this. Those that feel the slower, heavier bullet is the best and those that feel the faster, light bullet is king. This has gone back and forth for years.
The .45's reputation for a manstopper is long lived. There have been studies, statistics, cows shot, ballistic gel shot by the ton and the hits keep on coming. The 9mm got a bad reputation in regards to stopping power and the same tests and studies were conducted. It all comes down to a few basic things.
Modern 9mm defensive ammo has come a long way. Better and heavier bullets and so on. The .45 trend has gone the other way with bullet weights getting lighter and faster. To me it all comes down to your ability to place the shot where you want it and need it to go. Generally speaking this is easier to do with a 9mm. The trend lately has been to build the smallest gun in the biggest caliber. They are meant to be carried a lot and shot a little and this is not really a good thing. Just because you can stick a .500 S&W magnum in a snubnose revolver does not mean you should.
The choices you have mentioned are good ones. Personally I would stick to the full size guns for your first. Compact guns are great for concealment but again generally will not be as easy or accurate to shoot as their full size brothers due to their shorter sight radius and increased recoil.
Once you have mastered that then move on to something else. I carry a gun professionally in nasty places around the world. It has varied in models from Beretta, CZ-99's, Browning Hi Powers or Glocks but I have always carried a 9mm and have been restricted to ball ammunition due to international law and the simple availability to resupply but I have never felt under gunned or has it ever let me down.
I realize that the restrictions that I face will not be a concern with you you have to realize the myth of the one shot stop does not exist no matter what the caliber. You shoot and keep shooting until the threat stops doing what he was doing that made you shoot him in the first place...period. Whether this is one round or twenty nine.
As has been stated the 9mm is cheaper to shoot so that could/would lead to more rounds fired which would generally lead to better accuracy with your chosen firearm. The .45 ACP is a great round and they make great guns for the caliber and I own several but when home I normally grab a 9mm of some type to carry. On the other hand my dedicated home defense gun before I grab a rifle is an M&P .45 with extended mags, threaded barrel and a weapon mounted light.
It has nothing to with the caliber the gun shoots well for both my wife and I and is amazingly accurate. As has also been stated get some training on weapons manipulation, clearing malfunctions, reloading and so on. Many places offer "tactical" classes for the new shooter and cover everything from firearms safety to drawing and shooting from unconventional positions.
Keep us posted on what you get