Hm. I still need to consider a few of the sets here, but I'm fairly sure my least favourites are 2 and 9, with 1 only close behind.
2 because so little of the set actually seems important. Duke is pretty irrelevant. Apprentice I'm trying to imagine encorporating, but can't really see it. Loan could be useful, but I doubt it'd help much more than a silver in most cases. It's clear that Silk Road and Crossroads are very valuable, along with Baron. So putting that all together, it feels like a very contracted board with too few interesting options.
9 seems like a group of power cards thrown together with some strong combos. It's probably a tough set to play optimally, but I think IW/G would be pretty close to it, and that's so boring and easy. A very delicate and cunning combo will probably beat it, but whether anyone could think of that in the space of a single game... I have my doubts.
1 is similar to 9 - IW/G is just that good. I like the attack-counter style of the other cards, which makes me like it more than 2 and 9, and a 2/5 here seems to open things up a lot more which probably biased my opinion. But overall it doesn't look all that interesting and the game that was actually played didn't seem all that exciting.
I'm leaning towards 3, 5 or 6 as my favourite currently, but need to think more about 7, 8 and 4.