1.Gawain.
The best mecha I've ever seen in anime.
Even if it isn't the most powerful one, it's still the best. And if you upgrade it...
I think Gawain would look nice with energy wings =). And Druid system is a win.
2. Shinkirou.
A little brother of Gawain. For his seek of power he lost some Epic Points, though.
3. Siegfried. The most powerful mecha in Code geass, IIRC. Even LA and SEITEN won't match it's power. Only Gawain stands a chance for being Epic.
4. Damocles. Well, i was lying. This thing can beat any KMF.
5. SEITEN.
Choice of "bad" guys. This is KMF that a single villain can use to dominate the battlefield.
But the pilot's personality ruins the awesomeness of this villain mecha
6. Albion.
The "White Knight" of KMF.
Pure win.
7. Vincent.
Universal KMF. Any color suits it. And it's powerful.
8. Mordred.
Brute force. Nothing can stop the wave of destruction from this monster. Well, you can outrun it.
9. Percival.
A sadist choice. It look funky, but this is something you don't want to meet.
10. Tristan.
Nice elegant mecha. Another "knight" of KMF. This mecha's older brother looks sinister. Oh, the seek for power~.