I need to purchase an external drive for time machine for my late 2015 fusion 2tb, m395 i5 iMac. I just don't know what is the best choice for me. usb 3.0 or TB2? HDD or SSD? The heavy files I work with are mostly photoshop, illustrator and to a smaller degree, iMovie, FCP for casual video editing. My budget is somewhat limited so I can't afford something that is very expensive, so I would like to spend my money on a cheap but reliable external drive that will cover my needs.