I like the idea of Winnow more than Abandon. Abandon has a few problems:
1. It is really swingy. If you can get it early and trash a ton of bad cards, it could be really good. Otherwise, it's not that great. I rarely would expect it to be bought during the game if you open 4/3.
2. Loses power late. Even if you want a treasureless deck, once you have a Province you won't want to use it.
3. Would never want to buy it with cards that make you play it. Throne Room and Golem come to mind.
4. Once you use it once (maybe twice), it will likely be a dead card. I guess you could say Chapel also has this problem, but at least with Chapel you can choose what to trash, which makes it better than Abandon at trashing mid-game Curses, etc.
Because of those flaws, I would say Apprentice is way better than this card, though they fill different roles. Abandon can really only be used as an early-game trasher of junk, where Apprentice is one of the better trash-for-benefit cards in the game.
Winnow also has problem 3. I would recommend changing it to "Trash up to 2 cards from your hand" or "You may trash 2 cards from your hand". Trashing 0 or 1 cards won't help you much, since you'll have a small draw, but at least makes it so you don't have to worry about trashing good stuff.