Things that I look for for choosing one to vote on:
1. Does it look like a "Classic" House, in that other people would want to live here?
2. Does it have too much personalization?
3. Does it have space to customize?
4. Is it easy to move around in?
5. Does it meet the name Castle or Keep in some form?
Going with the classic theme, I think its easy to see many that are done up amazing, but just offer way too much customization and personalizationto work as a home that may be duplicated EVERYWHERE. Think about that, there will be more than just your custom house, there will be many of these. Open spaces, with correct building tile could be big to allow for the crafted granite to create your own rooms and style.
I also think its important, being a classic house, that it looks like, functions like, and feels like a classic castle/keep. This means overuse of water features, grass covering the room, rooms on the roof, being one big giant cube can hurt their function (though I did choose a few that had these things, done well enough to overcome or they do fall in line with the flow of the house). Footprint I think is very important for a classic house. They are all recgonizable immediately, These winners should be too.
Another point I hit was the number of flaws. Misplaced windows, stairs leading to door openings that dont line up, and things of that nature that render the aestethic of the house rough or the usage of areas non-functional ruled out many. I got the feeling some were overwhelmed with the amount of time it took to customize a 31x31 plot, and rushed many pieces that do stick out.
These are my favorites below, there were twice as many, I cut them down based on some of the criteria above:
Castles
32 - Pink Floors bugs me a bit, otherwise nice gothic style
59 - nice, simple, different, gothic style makes for a nice castle
136 - looks good, marble style is a bit off putting for a castle, but it is clean
141 - this feels like a non-cube medieval castle, and done up with room to customize =P
143 - simple, basic, a castle in a classic sense
178 - very nice, despite grass roof being a no-no to me. Cube-ish
206 - clean, marble. Not castlish, but more "mansion"
255 - an up to date take on the classic castle
285 - really nice castle, just wish there were stairs to the bottom floor
290 - similiar to 285, same problem
Keeps
19 - reminds me of wayne manor or something, but good design
35 - sandstone keep, and looks great. My only complaint is the upper rooms access
101 - the only "heavily detailed, personalized" one i think could make it, really nice
113 - looks like a keep, some unused space and stuff, but defined look
132 - like a sandstone mansion
187 - villa style, reminds me of a vineyard home
202 - sandstone take on a keep, looks great for something different but classic.
219 - like a villa on steroids, looks good
232 - its a keep, and has a defined look
special shout out to the guy who took a shot at recreating "Minas Tirith" though

if i picked 3 of each right this second:
castle
59
141
255/285
keep
187
202
219