personally I like heavier swingweights and heavier overall weights. I have my irons at D4 to D6. This is mostly a 'feel' issue for me, as a swinger I like to 'let the club do the work'. I really dislike a club that has a very light overall weight or very low swingweight. As for which is best, I'll leave that to the equipment guru's, but I think a lot of people are playing with clubs that are lighter than they should be - at least swingers. If you 'let' them, heavier clubs can keep you 'on track'.
That said, it is impossible to generalize. Everyone has their own 'ideal' specs for their motion and strength and there are trade off's between speed and mass.
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"Support the On Plane Swinging Force in Balance"
"we have no friends, we have no enemies, we have only teachers"
Simplicity buffs, see 5-0, 1-L, 2-0 A and B 10-2-B, 4-D, 6B-1D, 6-B-3-0-1, 6-C-1, 6-E-2