Metagross, for sure, by virtue of not only looking cool AND having a high base stat total, but also for its moveset including magnet rise, bullet punch and meteor mash, three moves I make extensive use of.
Magnezone comes in second for its steel/electric typing, levitate making it immune to ground, its sole 4x weakness by type, and whenever I can't hit an opponent on turn one, I like to make use of the lock on/zap cannon combo. Also, I mush like the damage/accuracy reducing effect of mirror shot.
EDIT: There is no steel type I don't love, though.
Metatang. I long to touch it's smooth head.
I like Metagross. One Pokemon ya gota love.
I also like Ferrothorn, 'cause it's looks like it can use Spikes and Leech Seed and stuff, and is perfect at that!
Empoleon! Amazing Pokemon. It's got an attatude like Sonic the Hedgehog!
Klinklang. I really like the way it looks and the name too! Haters gonna hate!
Ferrothorn. For ages I longed for a super-defensive Grass-type that wouldn't be screwed over by a number of weaknesses. I remember before Gen V thinking of the possibility of something Grass/Steel and thinking that would be terrible because of the 4x weakness to Fire... but back then I didn't consider all the types that combination would end up resisting or at least become neutral to. And now I see how ingenious the combo is, and for someone who doesn't implement a lot of strategy and just goes for the hit-it-until-it-dies routine, Ferrothorn inspires me to try out different methods of indirect offense and defense. It works amazingly well in tandem with certain other Pokemon, but its ability to Stealth Rock AND Leech Seed an opponent AND hurt most Pokemon that use physical attacks on it just makes it a gem on my team.
Not to mention it's one of the best candidates for a Trick Room set, plus that low speed gets put to good use with a good ATK stat and Gyro Ball. Ferrothorn's one of those "where have you been all my life" Pokemon. :D
(not to mention it's so friggin' easy to train as a Ferroseed WITHOUT using an EXP Share because of its excellent defenses and ability, so I rarely ever have to switch it out even if it's underleveled)
Escavalier, but I've never actually had one before, I just love its design.
agrron is my most favorite steel type.