My job afforded me the opportunity to test and use new desktop technology. At work we've deployed many. I've personally used the S3, SP3, SP4, SB, and the HP Elite x2. I've been using the SB for work exclusively for months. All of them worked just very nicely -- not perfect all the time, but really, we can't expect complex electronics and software to be completely flawless 100% of the time. The issues were minor and most have already been addressed by updates to the software and firmware. I don't think I'm especially lucky never getting a bad unit, because I think the vast majority hardware copies are fine. We have encountered actual bad ones, but so far the rate is less than 1%. For those owners who actually got one, it's a 100% failure rate for them and understandably they would be more vocal. For the most part, though, Microsoft's service is up to par (and sometimes superior).
Comparing the units, I would say this:
The S3 is good enough for light work, especially suited for note taking and non-computationally intensive course works. The option for built-in LTE is a plus.
The SP3 was my first serious Surface device. I used the heck out of that ever since Windows 8.1. It was a very enjoyable tablet, maybe even more so when running Windows 8.1. I know some would say that's heresy, but hey YMMV.
The SP4 is definitely a refinement on top of the SP3. Not significantly better, but better. The keyboard is better. But I missed the touch/hardware start button. I had gotten used to that with the SP3. It has a much improved processor as far as heat goes (it runs much cooler than the SP3) -- that alone is reason enough for the upgrade. Oh yeah, and Windows Hello....
The SB is awesome. With the dGPU it could even handle some actual gaming. The keyboard feels absolutely better. I enjoy typing on that keyboard sometimes too much. While I missed the old clamp style docking station, the Surface Dock is workable and almost just as convenient. The only complain I have is the ridiculously high resolution of the screen which sometimes means certain older applications that weren't written with high dpi in mind would be hard to read. Yes, I know about the compatibility options, but some just don't work. But that's minor, for me at least.
The HP Elite x2 was actually pretty good. But the processor is weaker and does not support facial recognition. Yeah, finger print scanner, but it's just not the same. The addition of USB-C is novel, but so far useless. I like the wireless docking option. I don't like their coat hanger kickstand, though. If you are looking for a cheap "Surface" this is definitely workable. If corporate IT needs a model that can be physically secured, this is definitely the one to buy.