Don't look at brands and the software included, look at processors and RAM instead.
While 4gb of RAM will work fine if you're working with JUST SMBX, if you want to start multitasking and stuff (SMBX, webchat, Paint.NET, etc) you'll be running into crampedness (?). So i'd recommend minimum of 8gb. Even if you say "well I won't be doing that" believe me, you will be in the future. Trust me here.
I'd also look into a quad core processor. SMBX itself runs fine on dual cores, but when it comes to multitasking/other gaming, quad cores are the sweet spot.
Those are the two main things you really need to look at. OS doesn't really matter, I'd recommend 7/8/10 (obviously).
So yeah, for laptops you'd be looking at probably something like
this. Yes, it's a little pricy. But 1: this has a touch screen. If you didn't want a touch screen, maybe
this. However, it's hard to make laptop recommendations because ultimately it's your laptop that you will be using/carrying around. I recommend their specs as minimums though. 2. You get what you pay for. Remember that.
If you're looking at desktops, you could totally get away with
this. This is honestly a steal for the price: 4th gen i5, 12gb of RAM. 1tb hard drive. Overall nice for the price. But you have to supply your own keyboard, mouse, monitor and possibly wifi adapter (unless you're hard wired).
And if you wanted to build your own well, you could go even cheaper.
And well, since you also asked what
I use, I have a custom built computer (built by me). I run a..
AMD A8-5600k Quad Core Processor @ 3.9ghz
12gb DDR3 1600mhz RAM
500gb HDD 7200rpm
AMD Radeon HD 7570 2gb (GPU)
Pretty soon I'll be upgrading to a GTX 960 for my GPU. I really recommend Intel processors though.
Trust me