I actually like using the units that come in at far too low levels. Babying is awesome.
And they end out awesome too, which makes me love it even more. Additionally, people who come in late are cheerful units.
Fire Emblem 9 is still piece of cake though, and I'm at chapter 22 now... People like saying stuff like "hard mode is hard" and "troll thread is trollish", but I disagree - "Difficult mode is normal/slightly easy".
I buffed up my Nephenee with 3 Dragonshields. I saw her being def blessed (she's bad at STR though), so it was a good idea. None of the non-boss or "elites" (in the groups) can damage her. I essentially send her in, she tanks all of them, and my other units nuke them. As she never gets the kill exp, it doesn't overlevel her (as a matter of fact, she's lower than the rest).
My Ike (who is 1 level higher) couldn't deal a single piece of damage to her with steel weapons. That's insane!
Edit: In FE6-11, I generally use the units I like the most, no matter the stats. In FE4-5, most units are pretty dull - so I generally pick a lot more from their power (which is pretty obvious, as their differences are enourmous).