Minho and Taemin have both changed a lot, and in a good way. Minho increased his dancing ability and Taemin has bettered his voice/vocals. I'm proud of them both because they are awesome! But if I had to pick one, it would be Taemin because his changed was meer obvious^^ Sarangheyo oppas!
I actually think Key because he uped +10 for style and fashion, which uped his already beautiful looks damn Key is hot now... But he was already a fashionista and impeccably good looking before the debut of Sherlock XD ~ But I agree with the commentaren made about Taemin and Minho, they have grown as individual talents...
Taemin, because he started out as an innocent, quiet, bowl-headed boy, with lacking vocals. But, now, he's funny and he's now one of the lead vocals (Like in Replay japanese ver)