Ok I'll bite on rats.
If the following 3 conditions are met:
-You're being cursed/looted (less necessary)
-There is (pretty good) trash for benefit
-You're making an engine
then rats will be pretty good.
Let's see:
Fishing Village, Oasis,
Rats, Horse Traders, Noble Brigand
Upgrade, Witch, Margrave, Lab, Horn of Plenty
(Besides Rats, all non DA because I'm not familiar enough with the rest of the set.) I'd like to try this: fv/silver and hope for $5 turn 3 or 4: get Margrave. Get a rats. Then get FV/FV/Upgrade on 3/4/5. Well, hold back on the rats if you haven't got enough upgrades yet. Don't play rats or buy rats if it would put your # of rats more than 1 over # of upgrades. Upgrade rats to Margrave or Lab depending on how many FV you have. Once you have enough upgrades (5?) hit the drawing cards, or move on to HoP.
You need like, five upgrades here, that's the big problem. It seems like a lot of work to upgrade your upgrade, so to speak. But see, I think the +1 card from trashing rats is big enough; I think it makes up for the times when I don't want to play rats. And rememember this is the bold predictions thread, I haven't actually played with rats