I'm no expert but would imagine that the G's from any Martin Baker ejection seat get the pilot out a hell of a lot faster than 20mph - and I understand the maximum number of times a pilot can eject is twice because of compression damage to the spine. So I'm pretty sure that landing vertically at 20mph is going to be considerably less damaging to the spine than (a) ejecting from a MB seat and (b) hitting something solid at 60mph.
So, given the the option, I'd be reaching for the chute every time!