Supreme Commander definatly made the best RTS units out there.
Especially their experimental units.
My first favorite is from the original Supreme Commander, the "Fatboy" mobile factory.
Four battleship cannons, anti-air placements, sheild generator, can go underwater, has two refuling stations for your air units, and can
make it's own army!
Hard to kill, unless you just had
more than the other guy.
Took awhile to get one built, but once that was done and you set it to work, it did everything on it's own. Simply drive it a few miles away from your enemies base to let the battleship cannons shred the first defensive line, and as that's happening you've built an army to penetrate the second line of defence as you move in...
My second favorite unit is from Supreme Commander 2.
It's the Cybrannasaurus Rex.
A robotic dinosaur with missle pods and cannons that can breathe fire?
Hell yeah!