I usually don't accept any of the computer's units. I always design all of them.
I usually have 8 kinds of military units, and I name them with a code name and a number - the number changes everytime I create a new unit of the same kind. Technological advance, for example, makes a Panzer 2 obsolete so I create the Panzer 3.
Here are my 8 models:
-- POLICE KORPS 1, 2, 3, 4...
Infantry chassis unit with weak laser guns, the best armor I can build and non-lethal methods. It's the police force which keeps my cities safe and avoid drone riots at the same time.
--- PANZER 1, 2, 3, 4...
Light cheap rovers with powerful weapons but no armor and no special abilities. They are my assault forces and I keep many of them in my border cities. If any enemy attacks me, I just throw them as a first shot to weaken my opponent. It's quick and cheap to produce, good for counter-attacks and quick assaults. They also destroy city garrisons as well.
--- HEAVY TANK 1, 2, 3, 4...
Expensive unit for land war. This unit has the strongest armor I have and the strongest weapons too. Special abilities (which depends on what abilities I have available). Hover chassis. It's an exopensive stronger version of the Panzers. Heavy Tanks are usually deployed late in a war, after I have lost many Panzers. Sometimes the war ends before I can finish building a Hevay Tank.
--- DREADNOUGHT 1, 2, 3, 4...
Expensive seaship with heavy armor and heavy weapons, but no capacity to transport anything. Cruiser chassis. I usually build 5 of them and order to patrol the waters of the world. When a war begins, all Dreadnoughts have the same mission: to stay in the waters between me and my enemy, bombing his cities and sinking enemy seaships.
--- PLASMA, IMPACT, SHARD... FIGHTER
Air unit with strong weapons and no armor. Special ability: air superiority. This unit has the mission of destroying all enemy airplanes.
--- PLASMA, IMPACT, SHARD... KAMIKAZE
Air units with heavy weapons and no armor or special units. This kind of unit has the mission of bombing enemy cities. I always try to save the planes from crashing, but sometimes it is just worth losing a Kamikaze so I can take a base.
--- JUNKER 1, 2, 3, 4...
Small cheap seaships with foiler chassis, light armor and heavy weapons. I use them to attack and invade sea bases.
--- MASSIVE INFANTRY
Infantry. Laser or Impact weapons. No special ability and no armor. This is my "desperate situations" unit. It's very cheap and I can build one per turn. When an enemy city is undefended and I don't have any unit to take it and no conditions to build an unit, I build a Massive Infantry and use it.
Also when I am desperately attacking an enemy position I sometimes deploy Massive Infantry to enlarge the number of my units, and kill enemy formers and colony pods.
And there are always the other units for peaceful uses. I always have a Former and a Fungicidal Former, and "sea versions" for both of them. Colony pods, sea colony pods... and that's all.