Best site for finding office space?

Where is the best place to look to find a small (1,500-2,500sf) office between Canal and 14th street, preferably loft-type space? Craigslist seems hit or miss (mostly miss). What about subscription sites like Loopnet and CoStar? Do they overlap? Which is better? Anyplace else to look? Last question, any chance I can rent in a residential condo building and use it as a pied-e-terre but with 1 or 2 employees there every day? No clients or other foot traffic. As far as I can tell, StreetEasy does not offer "live/work" as a search option for screening listings.