Re: I will buy a Mac Mini . Which one is best? Newer 2014 or Late 2012?
The 2012 model has a variant with a quad-core CPU so if you need that quad-core i7 you will want to look at the 2012s. They are user upgradeable, which is great, but they use the relative old Intel HD 4000 GPU so if you're doing anything that needs 3D graphics (rendering, games, etc.) it is probably worth the trade-off of user replaceable RAM to go for the 2014 model so you can get the Intel Iris GPU, which is a much better graphics chip.
For the 2014s, the base $499 model is comparable to an MBA and the base $699 model is comparable to a MacBook Pro. The hard drive can be replaced but it is a very difficult and warranty-voiding procedure so unless you are pretty good with your hands, I do recommend you purchase the internal storage you want at the time of purchase.