Given that you can get 512GB M2 SSDs now, I'd say go for that if you're worried about reliability. From what I've read, SSDs are more reliable unless you're trying very hard to wear out their endurance (on the order of 2PB according to http://techreport.com/review/27436/the-ssd-endurance-experim... )
but there can be some interesting not-a-failure modes, I know because I suffered one and the recovery was a nightmare due to overly-protective UEFI. Fortunately, anything on my local SSD is only in cache and not to be worried about ;) (and I managed to put the UEFI in dumb mode so it wouldn't interfere)
For the "not-a-failure" modes, are you referring to things like flipped bits? I had that happen on a USB3 high-speed thumb drive, where several of my source code files had random capitalization throughout the file (bit 6 was flipped on) and other weird corruption that indicated specific bits got either flipped on or off. But the drive was at 98% full when this happened too.
