Asia_Expat - 9:55 am on Jan 5, 2013 (gmt 0)
My main market is East Asia. My main competitor hosts in Australia, even though their bulk traffic come from East Asia.
I used to host in Singapore, but now have my server placed in a UK data centre (I get to use the iPlayer now :D but that's just a happy by product). It hasn't discernably slowed down the site for my Asia based visitors at all.
I'd go for Japan personally, if you already have hardware in place. (or Hong Kong, or Singapore)