While I'm certain I'm in the vast minority here, I'm actually using both and iPhone 4 and a Samsung Focus (WP7). I've played around a bunch with Android devices and nearly got a Nexus S but just personally not a fan of Android. I wanted to give WP7 a go and was able to pick up a barely used Focus on the cheap. Windows Phone 7 is refreshingly different--like the Facebook integration and Live tiles but it is still, IMO, not yet ready for prime time (though Mango looks like a huge step forward). My iPhone 4 is still my main phone (use Focus when I'm going anywhere a phone is more likely to get damaged, i.e. the beach) and I'll never move completely to WP7 but am curious to see how it changes/grows over the next year.
I plan to get the Focus next because I loved that S-AMOLED screen as well as the slim design. I see some refurbished ones being sold for $150 online with no contract.
I just got a brand new Palm Pixi Plus (AT&T) for $60 and really like webOS even though the phone is underpowered and lags. It really does make a great backup to my iPhone 4. Small and compact. I never had a QWERTY phone before. It eliminated my urge to get a BlackBerry Bold and Pre. For a brand new Pixi Plus that just came in June of last year for $60 is hard to beat.
A little bit of me is craving to get at least three more phones within the next 15 months. A WP7 phone like the Focus which I can get this year for cheap, an Android like the Xperia Play (to play emus), and a BlackBerry QNX phone by next year since the PlayBook really does have a nice OS.
So my starting lineup would by 2012 will be -
iPhone 4 (iOS)
Pixi Plus (webOS)
Focus (WP7)
Xperia Play (Android)
BlackBerry (QNX)
No thanks to Nokia N9 since MeeGo is DOA.
My iPhone 4 becomes an iPod touch and I will switch between four different phones when the mood is right and since they all have a removable battery cover. I was thinking of getting the HTC HD2 which can run multiple OSes, but I'd rather get the true experience that run the OS natively. I can live with a 1GHz single or dual-core for the next 4-5 years. Stuff like going quad core, 12MP cameras, and 3D screens is just overkill. The main thing I want from any smartphone is decent Wi-Fi browsing. I am not an app whore like I used to, so my attachments to any ecosystem like iTunes/App Store isn't there anymore. Basically these phones are like portable computers in our hands and my most used app is always the browser. So I can switch from smartphone to smartphone week after week and not get care of the OS it has as long as I am connected to the internet and I can listen to my music and take decent pictures. Some people collect baseball cards or jewelry, I would love to collect smartphones. The Swiss Army knife of electronics.