my fav fret wire is 6105 tall and thin... though i prefer steel frets over nickel
i like it tall because it makes it easy to do vibratos and bends, and yes, if you push too hard it will go out of tune, but if you have tight, thick strings, it will be a difficult task to pull off :P
i prefer steel frets over nickel for the sole reason that they last WAYYYY longer. My friend has had a guitar with nickel frets for 3 years, and has already had it redressed twice, and they're still chipping down. Safe to say he has alot of dead frets now, and it just doesnt play like it used to. Brightness in a guitar can be overcome with different pickups, thicker strings, or different choice of wood, so the sound change that the frets give doesn't concern me.