I have a 600 and 800 mechanical pencil. Love them, the feel can’t be beat - only by the (significantly cheaper) Pentel Graphgear 1000.
The other I really like is UNI Kuru Toga, the plastic one (shrug). The twist mechanism actually works; it is slightly wider thus more comfortable (for me) for longer writing sessions.
If you haven't already, give the Alvin Draft/Matic a try, imho it's up there along with them.