As I may have mentioned elsewhere: it's hard to compare, because Psion keyboards varied in their firmness. I have several Series 5mx units (as spares, for while others are being repaired — and yes, I'm still using one!), so I've seen how some are softer than others. (I don't think it's due to age; I think they were like that from the start.)
I hope to be able to compare them with a Gemini in a few weeks' time.
Is it possible that Jornada keyboards varied, too?
As to which is best, I don't think there's a simple answer. A keyboard that's too firm is tiring to type on; but one that's too soft can register unwanted keypresses. And the perfect ‘Goldilocks’ firmness may vary for different people.