So I'm on Seat #3 for the MkI.
The stock was a torture rack, a take off from a Cafe Classic was pretty good (not perfect, but much better than stock) and the OEM gel seat I added this past week as not much better than the stock one (ok maybe it's marginally better) - go figure.
Now I've heard good reports on the gel, so maybe it's a YMMV thing.
I know AF1 has some aftermarket seats for the MkI and II's ... maybe they have a decent one for the IIIs too?