Old thread I know, but I just wanted to say I'm very pleased with my 2014 Mac mini, for my business applications and mainstream consumer usage. I got the 8 GB model with 1 TB hard drive. It was basically unusable with the hard drive, but the NVMe SSD upgrade is extremely simple. A beginner can do it in less than 10 minutes, with very low risk of damaging anything, since there is no need to disassemble it. All you need to do is remove the back cover, with care to note that the Airport antenna is attached there, but you don't even have to disconnect that antenna. In fact, there is NOTHING to disconnect. Easiest upgrade ever. The cost for the 500 GB SSD + adapter was about US$50. You might to need to spend another $5 to $10 for the screwdriver, but I already had one.
The reason I wanted the 2014 is because Catalina is beginning to show its age now, as there was a fairly significant change in the aesthetics at Big Sur, which was further expanded upon in Monterey. The 2014 runs Monterey great. My 2017 MacBook is already on Monterey, and my 2017 iMac is on Big Sur but will be on Monterey as soon as 12.1 is released. It's great having my secondary desktop machine, the Mac mini, also on Monterey. And there is even a chance this 2014 might get macOS 13 too. It's really nice having current support, at least for a few years.
I would say that if you need raw CPU speed, the higher end 2012 models are better, but if you just need speed which is more than sufficient for mainstream business applications, mail, surfing, etc. then the 2014 can be superior, as it has the nice advantage of Monterey support and dead simple SSD upgrades. The only thing you need to be careful with is memory of course, since it's soldered on. I chose 8 GB because 8 GB models are common and cheap, but 16 GB models are out there too.
I paid < US$150 + import fees + shipping to Canada for my 2014 Mac mini with 8 GB and 1 TB HD, which worked out a little over US$180. Add in the new SSD + adapter, and my total expense was less than US$240. Granted, I got lucky with the eBay auction, but my costs are inflated vs. US buyers because of the extra costs to ship to Canada. In the US, these are commonly available for around US$225 with 256 GB SSD and free shipping in the US. For 16 GB you're looking at another US$50-$100.
People keep saying this, but out of all my old machines, I've only ever done it on my MacBook4,1 and my Mac Pro. For the former it was necessary to reduce fan noise, and for the Mac Pro I was doing a CPU swap anyway. For my MacBook5,1, MacBookPro5,5, iMac11,3, and now Macmini7,1 I haven't bothered, and they all run fine. In fact, Mac mini is basically completely silent with my usage.