So, I played Radiant Dawn 1st of all, in the Hard mode in the US version on my brother's Wii. Found it mildly hard in the beginning and quite easy by the end, since you have a plethora of very OP characters at your disposal.
My 2nd game was Path of Radiance, But I never finished it. 2 unfinished playthroughs in the US (Hard) and now just started a MM in the Japanese version, which I'm enjoying.
I've also played 2 FE games on gameboy, but don't remember their names, and recently, I played a little of Awakening and Fates.
The Lunatic mode in Awakening is really unplayable. It's exceedingly hard and any troops you have except for the stroger ones will die in 1 turn in contact with the enemy.
Now, the same Lunatic mode in FE Fates seems actually playable.
To sum up: the hardest mode in Awakening has gone too far and isn't fun at all to play. All the other Fire Emblems that I've played are kind of easy, Path of Radiance being the easiest (on late game it felt really like a boring cakewalk, which kills the game for me), and Radiant Dawn (which I've beaten, but will play again with a romhack to make it more challenging) being the 2nd easiest.