[Focus General] emjee87:
In the last year and a half, I've gone through a Nexus One, iPhone 4, Samsung Captivate, and now I'm on a Focus.

TLDR version at the bottom, since after writing this out I realized this is a mini essay..

Here are my thoughts:

Android is the OS you should be on if you want (nearly) complete control and lots of features not necessarily supported by your carrier (free tethering!). Unfortunately, assuming you're on AT&T, your options for serious Android phones are limited to a Nexus One or a Captivate. Between the two, I actually preferred the Nexus. Slightly weaker CPU, but you'll get updates pretty immediately, and it's a lot easier to mod that phone vs the Captivate. Also, I never had a single problem with the Nexus One as a GPS unit, but like many others my Captivate was sketchy at best when it came to GPS.

So far, the iPhone in my experience has the best battery life. I never really had to worry about it, and I'm a fairly heavy text/web browser/email user. It's obviously going to have the widest selection of apps, though that didn't necessary mean they were all useful. If games are your thing, the iPhone was also ahead of that by a long shot. However, without jailbreaking, it really is locked down. Tethering through AT&T's rate is a joke, seeing as it uses your already purchased data plan, and outside of changing your ringtones and wallpapers, you're fairly limited in customizations. Despite this, there isn't currently an option to tether at all on WP7.

Now having a Focus with WP7, I can say that the interface is very refreshing. Sometimes I just want to stare at the home screen because 1) the live tiles are cool and 2) the SAMOLED screen is amazing with a black background and brightly colored tiles. The web browsing experience is fast, but noticeably lacking compared to Android and iPhone (due to lack of webkit/html5). It's not a deal breaker by any means, but it was something I noted. The keyboard is about on par with the iPhone.

Build quality compared to the iPhone feels just as sturdy, in my opinion, despite the plastic body. It actually feels better in the hand to me, because of the curve back and slight lip on the bottom. It's also noticeably lighter to hold and carry around. So far the battery is holding up nicely with moderate to heavy text/web browsing/email/staring at pretty tiles.

Call quality was good, found the ear piece to be a bit clearer and louder than the iPhone. The biggest difference for me at the moment is of course the Marketplace. This is where the iPhone's ~4 years on the market really shows the gap. But given that this is Microsoft we're talking about, I don't expect their market to go the way of the Pre (which I also briefly owned) and be a barren wasteland (comparatively).

TLDR

iPhone 4 has ~4 years of exposure behind it with it's marketplace and iOS functionality, and it shows. Focus/WP7 has a fresh UI and is promising with Microsoft backing it. Build quality is very different between the two, but both feel sturdy and reliable. If you're making the leap to Focus/WP7 from an iPhone 4, you shouldn't have any big regrets, so long as you're not tied deeply into the iTunes ecosystem or your life depends on certain iOS only games.