First I began with a set of candidates:

  The client's _required_ list starts with all the protocols
  supported by every release in 0.2.9-stable through current
  master.

  The client's _required_ list starts with all the protocols
  supported by every release in 0.3.5-stable through current
  master.

  Everybody's _recommended_ list starts with all the protocols
  supported by every release in 0.3.5-stable through current master.

Then I removed the protocol versions that we do not actually want to
require or recommend:

  DirCache=1 (deprecated)
  HSDir=1, HSIntro=1-3, HSRend=1 (deprecated)
  (All HS* protocol requirements for clients)
  Link=1-3 (deprecated)
  LinkAuth=1 (obsolete)
  Relay=1 (obsolete)