[quote author=WheresMyElephant link
First of all, I'm a little confused as to which side you're arguing. First, you say that Watchtower only delays the equilibrium process, but then you mention how it depletes the ammunition, which actually decreases the saturation all together. Then you say that, with Mountebank, it doesn't even matter. If anything, it matters more.
I'm saying,
1. if your opponent takes a Mountebank and you don't, without +Actions a Watchtower is about the same as a Moat. Why? Without +Actions to play multiples, Mountebank's potency is going to drop off sharply once you once you have, say, 6-7 Curses in your deck. At that point it doesn't matter much whether the rest of the Curses are in the Trash or the Supply. "Depleting the ammo" seems irrelevant when the gun's jammed! (If you actually manage to block as many as 4 or 5 Curses you could maybe deplete the Curses while Mountebank was still dangerous, but that's unlikely). Never mind that even if the Curses did run out he could still give you Copper. Watchtower can delay the inevitable, the way Moat usually does, but we know that's not that strong.
2. If you DO retaliate with Mountebank, the Curses become more likely to run out. But like any Curser, if you retaliate you'd probably rather have Moat than Watchtower. If you have defenses and he doesn't, why do you want the ammo to run out? You're winning the fight!
But on reflection, I was wrong to say the so-called "equilibrium point" won't be much affected. Actually since Curses basically act as Moats themselves, a Moat (or a Watchtower) is basically just like having one extra Curse. Thus his Mountebank should crap out approximately one Curse sooner. So that's surprisingly decent I guess; you could probably make the case you'd rather buy a Watchtower or a Moat now than get a Curse+Copper later. The original point of this comparison was that Moat sucks and thus Watchtower must too; but maybe they're both a little better than I thought. Especially Moat on a $2 turn (the Silver test is probably a tougher question).
And no, I wasn't really suggesting you should intentionally take Curses as a defense. Just that realistically you're going to get them sooner or later anyway.
Edit:
With Moat, the number of curses (thus, the number of chances Mountebank can give you a curse) stays the same. Watchtower decrease that number with the trashing ability. That's kind of a big deal.
I don't really want to clog up this thread by arguing excessively in more posts, but you seem to be overlooking the central issue of my point 1. That is: it does not matter if Watchtower trashes a few Curses, because a single player playing a single Mountebank per turn generally wouldn't use up all the Curses anyhow. We could easily play a game where I Watchtower 2 Curses, you give me 7, but then my Curse discards consistently nullify your Mountebanks and the tenth Curse remains in the supply until the end. The Mountebanks became almost toothless without even needing to deplete the Curse pile, so what is so great about the trashing ability?
With most other Cursers, of course you'd be right. Witch can easily hand out ten Curses, even against Moats, and so it is critically important to reduce the Curse supply (usually with my own Witch of course).
Of course you're right that Watchtower's positive benefits are almost uniformly superior to Moat's (although again, it has the additional burden of passing the Silver test). I'm just comparing their defensive powers, which seem to be the main point here.