10% -- it's possible to find sponsor listings where you can do 5%, but those listings are prized and you'll pay more for them than for a comparable 10% down apartment.
Also, you didn't ask about closing costs, but if you are taking a mortgage you will pay a tax of 1.8% of the amount of your mortgage on a condo sale. Finally if you are buying in a brand new development, the sponsor will stick you with real estate transfer taxes (what we call RETT) of 1.4% of the amount of the purchase price.
I mention those two extra taxes only because they'll help you ballpark your budget.
author, "Diary of a Real Estate Rookie"
Insider Real Estate Tips with a Twist of Humor: http://tinyurl.com/2ag28z