I'd go for a Crucial or Samsung personally. There seem to be a few firmware bugs for the most recent drives, haven't had any issues myself but if it was my money I'd probably be leaning towards a Samsung right now. The 850 isn't the cheapest SSD available but they're generally quite reliable and they're good performers - not so much of a consideration for an older machine as you won't get the full performance anyway, but in the future you can always move the SSD to another machine.