Scanned through the thread & enjoyed both the wisdom & other comments. Noted many potential misunderstandings over the couple of years.
Least valuable military unit should be taken in a relevant context IMHO -- thus the warrior is judged as an ancient unit & the tank as a modern one & the twain do not meet. I agree with most of the consensus on the thread (i.e. the vet elephant (attack = 6) can take out a phalanx in a city, whereas a vet chariot might not. For 10 extra shields, the job gets done. So, if Im faced with any kind of early warfare, Ill research Poly before Wheel & wont even SEE Chariots (the chariot is obsolete with the elephant). If Im not faced with early warfare, there is a reasonable chance that the same research priority may still be in place, but the story in that case is not only do I not build chariots, but Ill also not build elephants.
Warriors have considerable relative value as early scouts & militia. Horsemen have value for chasing down Barb Leaders. Phalanx are reasonable defenders, but Im building fewer of them, due to a more strategic offensive mind set at the frontier. Archers
.hmmm I build about one archer per three games nowadays -- usually due to the need for some killing power early in the game (barbs & no local Non units on the island) & a hut gave me WC; similar thought carried one step farther with legions.
Triremes are best thought of as transport, but Ive killed a few barb leaders with them -- and early in the game the choice is crummy boats or no boats, so crummy boats will have to do. Not a bad unit -- after all at that point in time there are no other choices.
So for me, the question breaks down to job functions & choices -- what is the best choice for search -- Warrior, Horse, (Chariot, Elephant), Dip, or Explorer? Off the bat, the choice might be Warrior or Horse, but is the extra step of a Horse per turn worth the extra cost of 10 shields, and most importantly extra research time worth it for a Horse over an extra Warrior? Probably not (and thus even less so for the Chariot & Elephant).
Once a number of techs are in lace, more search options arise -- in a Republic, does one continue making Warriors to search (with a shield support & potential unhappiness Im reluctant to do so) or use one of the two middle early options -- Diplomats vs. Explorers? the Explorers cost an extra 10 shields to make & a shield to maintain but can go farther in the wilds. Dips might get sidetracked & do other services (like bribing barbs) & might get bumped back to the capital -- but I find myself making about an explorer per three games vs. a noticeable number of dips.
Early offense -- two move units are my choice over the cat/phalanx combo, but occasionally (once every ten games) Ill use the max offense to perform the mission. I cant even remember the last time I built a cannon (Cavalry is sooo much better).
Early defense -- again not too many choices -- either spend an extra 10 (or 20) shields or dont even pretend to have defense (which can be OK as well).
Middle game -- I usually get Tactics soon after Conscription & choose to build the stronger & more flexible unit accordingly for defense. I also often go out & do my first true invasions at this stage (hopefully my vet cavalry are facing nothing more than pikemen and sometimes even only phalanx -- easy wins).
As far as boats are concerned, I have never built a frigate (either use the galleon or use the ironclad) -- although Im willing to buy up barb frigates & go sailing with a dip for more None units. Ill make 0-6 Ironclads per game, usually for sea searches, with a view to upgrade them to destroyers for the same purpose. Once cruisers are available I consider destroyers as effectively obsolete.
Modern units -- Ill make a few arty units if Im still waging with cavalry & come up against walls or otherwise strong sites, but more often Ill just wait until the truly heavy stuff arrives. My eight pack attack squads are usually half howies, with a spy, tank, jeep & some other unit (whatever is hanging around & looking for experience) -- two squads will either surround the target city or blitz & take out four. I think that the special case for marines is so rare that Ive only built them in a couple of games -- (rough terrain, still in cavalry attack mode). I postpone flight to extend my Colossus effects & rarely see the need or use for aircraft as the AIs are smoke by then. In a recent GOTM game where I was in a modern warfare situation, the AI & I had all the techs, howies were cheaper than
stealth bombers for the city work & there was no need for any sea action; stealth fighters were not up to the task for taking out the defensive mech units, so they were not brought into the fray.
So for me, the least valuable units include: Explorers (use Dips), Chariots (use Elephants), Marines (use Cruisers & then Cavalry/Alpine; wait for modern tanks & howies), Choppers & Cruise missiles(use something else for the search capability/use land units or sea units for the combat.)