Meaner & sleaker, without doubt, but I still prefer the original. However, I must say that it always puzzled me why Steve Ditko originally gave the Scorpion a blunt, "smashing" tail, rather than a spiked, stabbing one. The scorpion itself has the later, obviously, so you would think that giving a super villain named after that animal a spiked tail would be a no brainer.

I'm a big fan of the Scorpion too. His first appearance in ASM #20 is probably my favourite comic of the Lee/Ditko run.

Mr.Freeze has had more than a few costume changes(as well as a name change) but my favorite was the design by Mike Mignola for Batman TAS:



It was simple but suitably menacing.

I always much preferred Sandman's original stripey shirt and brown slacks look to his later, more superhero-y look...

I've always had this image in my mind of Sandman waking up every day and opening his wardrobe to reveal a dozen or so green striped shirts and just as many pairs of brown trousers. Maybe he just doesn't want to change a winning formula.

For a while he ditched the brown and green and switched to a color scheme more in keeping with his teammates' ensembles:

Any update from the Mandarin's original costume was an improvement. Though they have gone overboard at times with giving him armor to make him seem more formidable against Iron Man. The whole point is that Mandarin has no need for armor, he can shatter steel with his bare hands in his martial art's training (exaggerated yes, but it is comics) and he has 10 rings of varying powers which make him more than a match power wise creatively against Shell head. Let alone Mandy's beliefs and philosophies pitted against mental battles with Tony.

Rhino's original look is all he needs. A total powerhouse who doesn't require the armoring and updates. Much scarier i think to see a big old 2 legged Rhinoceros charging at you. The psychological impact alone is that this bruiser doesn't require much more than his own enhanced strength and stubbornness to carry him through anything. He fought the Hulk regularly for crying out loud and kept on coming back for more!!! 

Whirlwind's 2nd green armored outfit designed by john Buscema (i think?) is better than his original spinning dervish look and the updates to Whirly's costume just keep looking more ridiculous. The only real good enhancement to him was the addition of blades at his wrists which would make him pretty damn rough and tough with out slicing himself to pieces.

Another Iron Man villain the Unicorn had a truly fugly original outfit which was somewhat made better in the 80's.
Same for the Melter's costume. What the heck was he trying to look like in that striped monstrosity?
Living Laser again had a pretty lame original suit and his revised armor look through the 70's and into the 80's was pretty cool until somebody had the stupid idea to make him look like his name suggests: a brightly glowing light show. Nice idea, but poorly drawn before the advent of computerized art and colors.

Certainly more to come...

Unicorn's costume update came in 1969, as I recall. As for Whirlwind, I liked his second look but I thought the mid 80s addition of a chainmail shirt made sense; from a purely practical POV, he'd have spent much of his time freezing to death in his shirtless costume.