Personally, just to put in my two cents, I think we may make the most money out of a Horse Market. Theres none up our way, and, well, I'm not sure how to explain my thoughts n.n. Im running on little sleep, but..
The party hall would be a very risky thing to run, as, personally..I dont think its making too much for the other towns, then again, I could be wrong.
And, with the guild house, I agree with others, not too many people would wish to run all the way up to Xi'an to build I guild.