I don't think you can tell what is the best unit at one to one battles. It depends on several factors. Such as: opponement, terrain, starting position etc. However I do have a favorite overall unit. The Minotauris. It has long range firepower. Effective against infantery and armored vehicels. It has a strong amor and is perfect for base defence. However it is not very fast and not effective against fast-moving targets. Every unit has +'s and also -'s