In practice, if you were dealing with a desktop that stays in one place, the odds of either one failing in normal use are low enough as to be treatable as equal. In either case, you want to do backups, and the likelihood of a failure is highest in practice when nearly new (unless you burn the system in for quite a while; most people won't.)

Since you're dealing with a laptop (or worse, a desktop that gets hauled around) the risk of mechanical damage to a hard drive due to an accident (drop, shock, spill, etc) is SO much higher than a drive failing itself -- even with the addition of accelerometers to park drive heads, which helps a bit -- that SSDs are almost immeasurably better (any hit that would damage them has almost certainly taken out your screen and probably the rest of the laptop case.)

Meh. It says that SSDs are less likely to fail but more likely to lose data. I'll take that bet anytime given the order-of-magnitude speed increase and battery life extension. And since I back up regularly, I'm not worried at all.

...you DO back up regularly in the 21st century, don't you?