The Mini 3 is the only iPad Mini generation I haven't owned, because ... let's be honest, if you're buying the Mini 3, you may as well just buy an iPad Mini 2 because they are virtually identical aside from TouchID. The Mini 3 was a rather pointless update overall, and I wouldn't recommend it to anyone.
That said, having owned the iPad Mini 2 and iPad Mini 4, it's hard to beat the power of an iPad Air 2 in the smaller form factor. I would choose the Mini 4 any day of the week, and it'll be useful to you for a lot longer than the Mini 2/3 would be.
That said, having owned the iPad Mini 2 and iPad Mini 4, it's hard to beat the power of an iPad Air 2 in the smaller form factor. I would choose the Mini 4 any day of the week, and it'll be useful to you for a lot longer than the Mini 2/3 would be.