The Baron and possibly the Lancer are my favourites of the newer designs. The visible lance just feels more "knightly". The Crusader and Castellan look pretty bad IMO: Never liked the positioning of the weapons...
I've recently taken a liking to the old Armadillo style Wardens though the old Imperial Knights never appealed much to me in general. The long legged one with the spike helmet was particularly bad IMO.
The Eldar Knights on the other hand are pretty awsome. The Bright Stallions and Fire Gales are brilliant IMO
?The plastic ones that came with TL, I converted to Chaos. ?Knights could go with a Chaos Force IMO. But I never really liked any of the G/W designs for Human or Eldar. If I was going to add Knights to my forces, I'd use BT models. ?But none of my armies are short units. ?Save for Chaos, "the Army that G/W Forgot", so that is why I gave my TL plastic Knights to the Dark Powers. ?
I acrually attempted to build a more mechanical looking one some years ago but the project never really got anywhere.
but the others are fine to me.