Last years Mac minis was better so I have been told, easier to update and had better processors. If you buy a 2015 Mac mini then you are stuck with the memory it have in as it is soldered in and the hard drive is almost impossible to replace. The older ones was also quad core, newer ones are dual core. No doubt they use a slightly higher tech CPU, but I think the lack of two cores would make a difference.
Also, while you can use a windows keyboard with a mac, it is not ideal.
I have been considering a Mac mini myself, but not sure to be honest. They are a different kettle of fish to a Windows based machine, best to go into a shop and have peak first.
I have used Macs a few times, so I am used to the way they work, well almost, but still feel strange from a Windows based machine.
Desktop machine now powered by windows 8 pro 64bit, no dreaded metro and Linux , laptop by Linux