Now I am going to buy a S&W .45 Any recommendations?
My third generation 4566 has served me well. It's been as reliable as reliable can be.
I wish S&W hadn't turned away from the steel pistols when they jumped on the plastic band wagon. The 3rd generations were pretty decent weapons as far as pistols go.
I also like barrels in the 4" range found on the 4566 rather than the longer 5" bbl's of pistols like the 4506. I find them easier to use as a combat weapon than the longer 5" bbl, but that's me.
However, a 5" bbl pistol like the 4506 will give you a longer site picture (more accuracy) and more weight to control the pistol. You just have to deal with the concealability of the longer slide/barrel if you'd be carrying it.
The bbl length preference applies to my S&W. However, it's an exception in my other pistols that the .45
ACP 
was named after. In those I prefer the 5" bbl. It just looks and feels right for me and is the pistol that I carry most often.
After all of that, you're going to get a lot of other opinions on what is best. We each have our experiences and prejudices, including those for and against the more recent plastic-framed pistols. For the most part it's going to be hard to go wrong on model that has some time under its belt to prove its dependability.
BTW, be careful of assuming that by referring to a .45 that people will know you mean a .45 ACP (Automatic Colt Pistol). There's another current pistol cartridge in .45 GAP (Glock Auto Pistol). They aren't compatible. Then, there's also the common .45 LC (Long Colt) revolver cartridge that's still popular.
Good luck on your choice of pistols!