Hi think there can't be a "preferred unit" for each game. Each game is different and u always need different strategies. And this is even more valid for the first part of a game. Say you love a ground unit and ur civilization born on a little island...
About a preferred unit, i think the spy has a great power. U can use it more than a single time, it is quite fast ( cos u have a spy when other civs already have plenty of roads and rails ), u can explore ur enemy, u can know all of a city and... god !
You can DESTROY a city either nuking or inciting a revolt.
In our last game me and my friend had the entire greek civilzation destroied in 3 turns using 4 spies. Greek werent a democracy so a veteran spy has a great chance of nuking a city.
About "true" military units, i think i am in love with stealth fighters but they are only in very long games.
About preferred early unit... no, i have not. There are many very usefull ones. A phalanx is nothing without a catapult and the oposite is also true.
I NEVER use explorers, frigades, dragoons.
I think in civ2 is easier to say what is useless than say wat is most necesary.
Bye
