Interesting topic idea, here's my best board:
$6 Fairgrounds
$5 Horn of Plenty, Rabble, Stash
$4 Baron, Bureaucrat, Scout, Young Witch
$3 Black Market, Oracle
$2 Hamlet (Bane)
Since my top ten includes Young Witch, I took my next highest 2 or 3 cost card as the Bane (Hamlet, as it turns out). The set seems to show my tendency toward big money-style games, but there's an interesting catch: my top two cards (Oracle and Horn of Plenty) are apparently in as trap cards...I play well in games where they are present by ignoring them. Bureaucrat also falls in this category (a card which I buy in only 2% of games). In fact, I only play 3 of these cards in 40% or more of games (Young Witch, Rabble, and Black Market), while 3 of them I play in fewer than 10% of games (Bureaucrat, Scout, and Horn of Plenty). As for how this plays out...I probably go Young Witch/big money here. Black Market is a little tempting, but it conflicts with Young Witch, which is the higher priority.
Worst board:
$6 Border Village
$5 Cache, Embassy, Governor, Haggler, Ill-Gotten Games
$4 Silk Road, Trader
$3 Oasis
$2 Fool's Gold
Given that these are all recently released cards, I think this set can be entirely disregarded. I think I know the cause...sometime within the last couple of months I switch from matching with any registered player to primarily using the +- 15 levels option...which in turn has caused my raw W/L rate to dip. Nothing terribly interesting there. If I exclude Hinterlands and Governor, I get the following set:
$8 Peddler
$7 King's Court
$5 Contraband, Tribute
$4P Golem
$3P Philosopher's Stone
$4 Conspirator, Militia
$3 Ambassador
$P Transmute
Okay, that's more like it. If my best set showed that I do well with big money-ish strategies and avoiding trap cards, this set sows that I still have a lot of work to do on my big engine play. I don't have as much insightful commentary here (if I did, maybe these cards wouldn't be so bad for me

). I've been working on my Ambassador play, but I'm still not very good in those games. Apparently I buy Militia far more often then I should, while Transmute and Philosopher's Stone are two card I'm not giving enough credit to (or, maybe not...I still play better without them than with them).
As to how I'd play it, I think Ambassadoring down to a Conspirator/King's Court Engine is the best bet here...but whether I could pull it off is an entirely different matter.