There is no such thing as the 'best' phone, only whats 'best' for you.
I think the Smartphone market is pretty much now gayPhone, Android or Win7 Phone.
Each has its own strong and weak points.
gayPhone, mega stable, intuitive, easy to use, "just works" as expected. But poor phone signal, esp in weak signal areas. Have to have gayTunes, which is appalling, and Apple's insistence that you use the device as they want you to use it.
Android. Open, but falling down exactly the holes Symbian did, and will go the same way if Google do not get their backside in gear. Generally less stable that the gayPhone. Probably the 'best' Android is the Sony Ericsson Xperia X10 (not the mini - unless you need this form, but does limit it).
Win7, still new, not sure I'd want ti be an early adopter.
Symbian is a has been. A decision to not include a user interface in the core OS means that it was expensive (in development) for OEMs to release, so pretty much only Nokia did, and with a weak interface. Interestingly, Google have chosen the same with Android, and are trying desperately hard to keep the source code closed.