You want cheap artifacts. These decks need early interaction and cannot afford to spend large quantities of mana not affecting the board. After all, in order to recur Witching Well you need 2U for Emry and then 3UU to draw two cards. That's such a massive investment that you'll lose the game. And if you want to use the ability again, you have to spend another 3UU mana.
Consider the following:
- Recurring Spiritbomb
twice is actually one mana cheaper than recurring Witching Well once.
- You can recur the bomb and draw without spending all your mana. It's unlikely you can draw cards with Witching Well and then affect the board.
- Spellbombs are cheap to put into the graveyard for Emry to bring back. You can't self-sacrifice Witching Well until you have four mana sources in play.
- Spellbombs affect the board. You can bounce their creatures, yours or use it as a counterspell against removal.
- Spellbombs can by cycled if you don't have (or can't spend) colored mana.
The cards I use to support Emry and other similar cards are:
That said, I don't run Aether Spellbomb because the artifact decks are not very interested in bounce.