Only way to know for yourself, is to really try for yourself...
Unfortunately, all opinions asked are biased no matter which way you look at it.
Your "preferences" may not resonate with those of the person next to you, so you can never be sure that his opinion will resonate with yours.
So there is only one way to find that out: to try all platforms and see which one YOU prefer...
Sounds harch, but basically regarding this subject you can really only trust yourself.
My own opinion :
WP
pros
cheaper models that are still "on par" with higher models.
smooth polished and fast UI, tries to be "innovative".
has some "uniqueness" to it
cons
lacks WAY too many features
truly basic "needs" are not met at all (calendar/music player/video player,...)
lots of garbage/fake apps in store
pretty useless as a company phone
ANDROID
pros
"free" user experience
has about every feature you'd expect from a "SMART"phone
the latest models are VERY fast (even faster than WP. Really!)
Much more choice of apps in store
cons
MESSY UI. Opposite of "innovative"
The OS is cloggy, not that efficient.
cheap models are def. NOT "on par" with higher models.
iOS
pros
really def. preferrable as a company phone
BEST mp3 functions and sync functions in general.
Stuff like jail breaks for those who are into that.
cons
WAY too expensive considering fragile build quality.
Similar limitations as WP (isolated storage, sms-tones,...)
Like all porches, they all look alike. No real "innovations".
BB
really don't know, cause I never tried one of those, but I do know they are also perfect as a company device.