Nokia has switched to Windows Phone, Symbian is on its way out.
Between Android and Windows Phone, just look at the number of Manufacturers or Phone Models that use them. Android is a clear winner there.
According to wikipedia:
Over the course of 2009–2010, Motorola, Samsung, LG, and Sony Ericsson announced their withdrawal from Symbian in favour of alternative platforms including Google's Android, Microsoft's Windows Phone.[71][72][73][74]
In Q2 2012 according to IDC worldwide market share has dropped to an all-time low of 4.4%.[75]