[Sinkhole]

I would suggest you think about going with an M&P40 again and consider purchasing the factory 357Sig barrel, giving you the option to have calibers. the barrels sell on sights like Midway for around $78. A meager investment to have 2 calibers. You can also convert the 40S&W M&P down to 9mm with a simple barrel change and using Factory 9mm mags. This would give you the choice of 3 different calibers for the original price of the gun + under 200 more. Having the ability to shoot 9mm will save you in ammo costs but still allowing you to shoot the same gun giving you more trigger time with the same platform. And unless you had some major dislikes, you are already familiar with the gun. This is just my opinion. There are a lot of good firearms out there to consider. I suspect you will get a lot of 45 is best, 40 is best, 9 is best, 357 is best. Do your research, there is no perfect round that's great at everything or we'd all be using it. This is why I personally give a lot of merit to a multi-caliber system. I think it allows more flexibility. If you want to go 45, I would also recommend the M&P45 I love mine and have 5 10rnd and 2 14rnd mags for it. I also added the Apex DCAEK kit, which made the trigger like butter.
The down side with going with a gun this size is it's harder to conceal. I rarely carry my M&P45. My usual FS carry gun is an FNH FNX-9 and I carry my Ruger LCP when i need to pocket carry or deep concealment.