I don't have a clear-cut favorite - I have a older Droid X and also an iPhone 4s - both platforms are great - used to have a Blackberry Storm 2, it was great but seemed to get old real fast compared with the other two.
I enjoy the option of using both types of platforms for basically the same thing - but obviously they are different platforms - one is more open sourced than the other - but compared to a few years back in the mobile platform OS's - these two are excellent! I had the older Palm PDA devices - they were great, still have one I use as a clock - wish their platform endured past the HP mess as I feel the Palm platform could've still been popular - as long as it was marketed to meet the demands of today's mobile consumer.
Have to see about the Microsoft phone - in the past it would take them a few releases of something to get it right...
Of course 20 or so years ago, all the phone did was power up and allow one to make or receive calls - no text messaging or anything else - not much was different in the various models offered. Probably in another 20 years people will wonder how we 'survived' with the current state of mobile phones!