Now I know we have the 45th unit one but that's down at the bottom of the top unit list, so what about nearer to the top of your list? The reason I'm not saying the best unit is because there will be quite a few players who are low levels and have the best unit in the game so it would probably make this list unbalanced because you could have a level 75 saying they have an Aeon, Sun Stalker and then another saying they have some sort of 1000 stat unit, anyway enough rambling and I shall start...
Level 118
5th unit: SL-65 AS Jet 2300/1800
LLP - Level 15
5th unit: Poseidon UCAV 1229/819
Edit: I should also point out that I played this game ages ago, so long ago infact that battle points were completely a new thing, let alone factions and stuff. I was very weak then so I quit and came back about 4 months ago or so and I still need to catch up with a lot of people around my level.