Hard handles, without any doubt!
The soft ones pick up grease and oil which is hard to wipe off, then they get grit, then the grit wrecks the soft inserts!
I've seen the older hard handles put up with decades of use. Many of the soft Instinct handles that have seen more than about 6 months of daily use just seem to be a greasy blob! There are exceptions, and if you do electrical assembly or somesuch you might prefer the soft, but for the average wrench turner, choose the hard!
From time to time there are sets of the old style 'all hard' handles on the van! These are well worth acquiring, and perhaps the best mechanics driver ever!