I feel that a good mix of all units is best, so there are no blind spots or bad surprises when the enemy finally decides to go after me.
Otherwise it depends on the faction I'm playing.
If I'm a Gainans, then worms are cool.
If I'm a science faction of course I go straight for MMI.
If I'm Yang or Miriam, well, just overwhelm your opposition with higher numbers.
Don't really use naval units much, if I can avoid it, but they can be fun. Especially a sea-former working on enemy territority.
Oh, I miss hover-tanks and missiles in your question.
Anyway, if I really have to decide, I'll choose copters. Copters are the key for an easy win. "Death from above."
To bad that the AI doesn't really know how to use them correctly and often lets them stay in the open because of short fuel.