Some of it has already been said, but here's my opinion on the Knights anyhow:
I don't like them! But not really for the differences between the individual knights, which don't seem to be that strong to me - at least compared to Tournament and Black Market. (Well, I guess Dame Anna (trashing) is an exception if she can be bought early on boards without other trashing, especially when there are Cursers and/or Looters.)
I still don't like those differences too much although they are comparably weak, but this mechanic also has interesting implications and the individual names sound kind of cool, so overall that is OK for me.
But what makes me dislike it is that the card is still terribly luck based! I think overall more luck based than every other card (maybe except Treasure Map).
I predict that at least on boards heavy on Dark Ages (with
7 cards with relevant on-trash-benefits), the Knights will usually be very weak because their attack which even on other boards doesn't seem too strong on average to me has a decent probability to actually be really *useful* for the opponent.
So while weak on average at least on Dark Ages boards (and I
think even on many boards without on-trash-benefits), the attack is
highly luck dependent, so that (weak or daredevil) players which go for the suboptimal Knight may very well win on that decision alone anyway. (Kind of like with Treasure Map for which I dislike that as well.) You can hit a Fortress or other on-trash-benefit-card, but you could also hit and trash the opponents early Gold or Mountebank or Witch or whatever.
Just the extreme difference between these too scenarios should be significant enough to decide most games.
I mean, it is about as bad as swindling the early Mountebank or Witch into a Duchy compared to kindly removing an opponent's Estate from the top of the deck - but I also hate that about the Swindler and it should be more likely to happen with a Knight given that it attacks two cards and also hits $6 cards badly (and not just $5s).
Even on boards where going Knight is the best decision because it can be expected to give the best bang for your buck
on average, getting unlucky with it by only hitting Estates/Shelters/Coppers/Ruins/Curses/etc. is still highly luck dependent.
I think that Dominion has enough luck based aspects already, having more cases of such extremely different outcomes of playing a single card is bad IMO.