Definitely Knights... dead-end tech, and not much better than Chariots. (I never build Knights in Civ II either.) For mid-game, I really wish I got to keep Cavalry instead! Half the cost, and what I really want is a fast cheap scout to complement my Musketman/Rifleman and Cannons. If it was possible to mod Civ I I'd have made Cavalry not expire until Mobile Warfare.
I love fighters, for the multiple attack capability. And if you've almost conquered the world and have enormous production abilities but can't research worth crap, 20 or 30 Fighters can sometimes take a city that has city walls. (Yeah. I still remember that game. One city left, but it had city walls, I just kept throwing Fighters and Cannon at it.)
I've been frustrated with Cruisers... I had some keeping an eye on things, on an Earth map. I was the Americans, the other big power was the Russians. A couple of my cruisers observed a Russian fleet of battleships escorting transports to Australia. I could do nothing! My cruisers just watched as Russian armor seized the whole continent. It was over before my expeditionary force was ready to leave port... cruisers are too weak to engage either battleships or armor, so I was helpless.
On the other hand, my battleships, transports, carrier, bombers and armor captured Australia back even faster than the Russians had taken it the first time. And once I did that, Delhi (in its historical location) defected from the Russians to me and I spent the rest of the game defending India against Russian attacks, until I built my spaceship.