I have personally tried everyone of the OS stated in the title of this post except for the Android. In fact there was another - Palm - which I deliberately left out as it is already out of contention, I believe.
What would be your choice? I find the iPhone OS is very stable and user friendly. Looking at it reminds me too of the Palm platform which is kind of similar with the icons arranged in grids.
Windows mobile is actually quite good but one needs to be ready for it sometimes "hangs". Symbian too is decent but I have experience my phone "hanging" as well.
But to make a fair comparison, one needs to look into the hardware as well for newer gadgets would normally be using a faster processor.
These are my thought on the smartphone OS war.