I just play casually, because I would find that, unless I specifically want it, challenges that aren't imposed by the game itself hinder my fun.
I generally play what is considered to be the normal mode of the game, so I have a semi-decent challenge.
Also, generally, fallen allies don't stay dead. Unless I'm doing a Gaiden run of Shadow Dragon.
I also prefer growth rates in characters, mainly because that's one of my favorite parts about FE: seeing even the wimpiest characters grow up through harsh training into decent combatants.
Finally, my favorite class is the Dracoknight/Wyvern rider classes, due to the fact that they usually have really bulky and good stats, they have amazing movement, they can FLY, their biggest weakness can usually be negated by an item (which is why I enjoy the Iote's Shield), and there are generally no really BAD Dracoknights in the series. Sure, there are some ones that are below average in terms of quality, but even then, they're usually quite good.