As of now, I've voted for Prefecture. I think it could maybe be cheaper, but overall I like it better than the other options.
Landlord
Types: Action Victory
Cost: $5
+2 Cards. You may discard a Victory card. If you do, +1 Action.
Worth 1 VP per empty Supply pile.
I find both the top and bottom of Landlord to both be pretty uninteresting. The top is a weak sometimes-Lab and the bottom fluctuates between 1 and 3 VP in most games. Not exciting to me.
Overseer
Types: Action
Cost: $4
Put a marker on an empty District of the Overseer Mat. If you put it on the
Residential District, +1 Card and +2 Actions
Craftsmen's District, +3 Cards
Commercial District, +1 Card, +1 Action, and +$1
Industrial District, gain a card costing up to $4
Logging District, +1 Buy and +$2
If four districts of the mat have a marker, remove all the markers.
Rules Clarification: There is one communal Overseer mat, split into the five districts.
I like the concept of Overseer. I can't speak for everyone else, but I personally probably won't be printing my own custom mat for it. Sleeving proxies is tough enough. I'd like people to be able to just buy a copy of Alchemy and proxy up this set, and Overseer would make that tougher.
Monastery
Types: Action
Cost: $4
Gain a card costing up to $6. For each $1 over $4 it costs, each other player may choose one: he trashes a card from his hand; he gains up to 2 Coppers, putting them into his hand; he discards his hand and draws 5 cards.
Monastery is clunky. Cool concept, but I'd rather see a cleaner implementation like, "Gain a card costing up to $6. Each other player may gain a card costing at most $2 less than it."
Homestead
Types: Action Victory
Cost: $4
+2 Actions. Reveal cards from the top of your deck until you reveal a Victory card. Put that card into your hand and discard the rest.
Worth 1 VP.
Prefecture
Types: Action Victory
Cost: $5
Reveal cards from your deck until you reveal a Victory card. If you do, put it and one other revealed card into your hand. Discard the rest.
Worth 2 VP.
Homestead is sort of like Prefecture. Perhaps a happy medium between the two would be best. Like a Prefecture that gave +1 Action, but was only worth 1 VP. That might be a cool Lab variant. Between the two, I'll take Prefecture.
My favorite card submitted was jackelfrink's Liege. I really like the "play this again" mechanic; it's something I've been trying unsuccessfully to fit into my own cards. I also like that it's a mild "attack" that is often just using your opponents' hands to draw you cards, rather than actually hurting them.
Liege
Types: Action Attack
Cost: $5
+2 Cards. Each other player discards a Victory card (or reveals a hand with no Victory cards). If any player discards a card this way, play this again.
I agree with those who said it really anti-synergizes with Intrigue cards, though. Even more than Tribute, it makes you not want to buy Great Hall, Nobles, and Harem. I'd like to see it in the next Hinterlands contest! Cool interaction with Tunnel.