The correct one is 303.
I use it and haven't found any compatibility problems with UAs newer than Netscape 4 (1998, released 17 years ago).
If you use 302, you're risking that UA will re-send POST to the new URL instead of switching to GET.
Still, if you're worried about HTTP/1.0 clients (which don't support vhosts and probably won't be able to access your page anyway) then you should include HTML with link to the new page in body of the 303 response (web servers like Apache do that already).
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…