It's still good.
You should still buy it.
If you don't, you should still have a good reason, and I mean a REALLY good reason.
"But there's trashing!" - No, every Curse they trash is a Copper or Estate they didn't get to trash.
"But the trasher competes at the $5 price point!" - You may want to buy the trasher first, but if you do, you should probably still buy the Witch later.
"But Mountebank is in the kingdom!" - Actually, after you play Mountebanks a few times, they block it often enough that you probably want to buy the Witch to hand out the rest of the Curses.
"But Moat is in the kingdom!" - Having a Witch still threatens handing out Curses. They only have to fail to have Moat once to get punished for it. And if they buy a lot of Moats, then you've hurt them in a different way: they spent a bunch of Buys on Moats.
"But Lighthouse is in the kingdom!" - Okay. The Moat principle still applies - they only have to miss it once to get hurt. However, it's a lot more okay to have lots of Lighthouses, and in some games it's even beneficial (i.e. Minion games). So sometimes, they do have enough Lighthouses to make buying Witch redundant. But if you notice they've gotten complacent and are starting to miss Lighthouse turns, maybe you should reconsider that Witch...
"But Ambassador or Masquerade is in the kingdom!" - These do counter Witch the most regularly. It
sucks when they give you back a Curse.
"But I'm drawing my deck, and I have a trasher, and I'm out of things I want to trash with it! I'll just trash the Curse if I get Witched!" - Sure, this is true for now. It's easy for this to stop being true, as you add payload or VP to your deck. Much like the Moat argument, if they're playing Witch every turn, you only have to fail to draw your trasher once to fall behind on having a thin deck. Once you fall behind the first time, it's more likely you fall behind the next, and soon your thin deck has 3 Curses in it. It's a classic recipe for beating people who are overconfident in their deck's reliability.
A lot of new players don't like Witch, because it slows down the game. Most people's idea of fun is getting to play a bunch of cards and produce a bunch of money. Witch gets in the way of that. But I like Witch.
When I give out Curses, I think to myself "yes". When I get Curses, I think to myself "no". Even if you don't like it, you have to respect it.
Sometimes, you
can skip Witch, and you get to be a Hero. Maybe even a Champion. Just be careful out there. Curses make the world a scary place.