To me, the nicest OS will be BlackBerry OS 7. RIM bought out The Astonishing Tribe (TAT) which makes amazing 3D interfaces.
TAT BlackBerry PlayBook Apps
http://www.youtube.com/watch?v=rNISlsdXIdI
BlackBerry PlayBook Ad
http://www.youtube.com/watch?v=WAHY6Ahyv4s
I think the PlayBook looks more professional-looking while the iPads and other tablets look more consumer-ish and look like giant phones catered for kids and wannabe yuppies (corporate poseurs). PlayBook has a better name too.
Even the iPad has the name of a spoof on MadTV from 2007! Who wants a tablet that sounds like a brand of a female's menstrual pad?
My next dream phone that perfectly compliments my iPhone 4 is if Sony Ericsson and Google make me a Nexus Play by this year or I will be stuck with another OS for 20 months after my next upgrade next Feb. Why Android? It is laggy, right? Because it is peaking right now, can always improve, and PlayStation games and an unlocked, stock Android can lock me up on their ecosystem. One of iPhone's biggest weaknesses is diversity in game genres because it lacks a gaming pad. Once I start paying $10-$20 PS2 digital downloads for my phone, I could be stuck with PlayStation phones forever because I am NOT going to throw my library just like that. But Sony will "F" it up again and ask for a prohibitive price tag like the $900 for Spain. XPERIA PLAY is already going to be their next failure to launch. Sony should look at iPhone 4's weaknesses and either do the opposite or improve on their strengths.
With BlackBerry or WP7, I can always leave because their app market is still immature and have no apps enticing or hardware features enough that I can't find at equal value with Apple's App Store or with an iPhone. Android, while laggy, is still the one with the future and more versatile of all the OSes. They seem to push cutting-edge hardware the fastest, but you need it stock. If iOS is like a safe Disney World and Android is NYC, I can always find the safe and classier spots of Manhattan.