iPhone
Mine is starting to slow sometimes, I feel as the iOS is being moved further away from it's hardware state. Said software's a lot more suited to the 3GS or 4 with the faster processors. The thing that attracts me to an iPhone 4 is the speed, display and camera. The speed as it'd basically make the experience I have so much better (and it's pretty good already), the display as it looks even more impressive than it already does and the camera as even though it's "only" a 5MP camera, I've always felt the iPhones sensor/software combo makes rather good use of the MP count. Plus the HD video is pretty amazing for a phone camera - really smooth and not at all what you'd expect from such a camera. You also have the Apple Stores that give properly good customer service and the ability to avoid O2 shops, which is pure bonus.
Downfalls though - price - as with everything Apple you pay a lot. Upgrade for me paying £35 a month is £139 for the 16gb iPhone 4. I got my 3G for free as it was a refurb which was every bit as good as a new one. Secondly, there's the iTunes experience on the PC, which is pants. It's nicer to use than WMP or similar in terms of music playing and the like but I just don't enjoy it. Thirdly, you can't muck around with the software in as in-depth a way as you can with other phones. But then again, that's how Apple like it - unless you jailbreak of course :wink: Fourthly, it's a finger print magnet and even more so with the glass on front and back. You can get Gelaskin covers though that address that. Finally, though the glass is tougher any other iPhone (you can even scrape the front with a knife apparently if you feel like it and not get a scratch), it can still break if you drop it. But then, most touchscreen phones have that issue.
Android
I've been looking at these for a while and the latest 2.2 update seems to have helped a good bit with the OS stabilisation and a few other aspects users wanted/needed. Still not sure about the app marketplace organisation with software compatibilities and such but I'm guessing that could've also also improved. I like the look of the OS and the phones too, the HTC Desire has also appeared on my radar and given it costs £59 on my upgrade, I'm definitely considering it. However, the camera's nowhere near as good at pictures and video compared to the iPhone 4. Some of the apps aren't as polished either I've been told too but then that's software more than hardware. I've seen some nice stuff on Android and the openness and adaptability I've seen really attract me to it. Some phones seem better than others though, for my money at the moment, HTC Desire and the Samsung Galaxy S are perhaps the best ones out there.
The Dell with Android OS is the Streak, which actually intrigued me due to the ludicrous 5" screen. Honestly, if you use it as a phone, you're bound to get a few Trigger Happy TV impersonators around you. That big screen does look good though and having used it in the CPW, it does seem pretty smooth. Uses the same processor as many of the other Android phones (Desire, X1, and in fact the WM7 HD7) - 1GHz Snapdragon.
Windows 7 Mobile
Never thought I'd even consider a Windows Mobile OS phone but here we are. I've seen them in action though yet to play with one but from what I have seen they're rather speedy and pretty slick in the operation. Loads of animated navigation though which could become tiresome. Explorer, Zune (WMP), XBox Live, MS Office - just a few of the well known MS names involved in the OS. Again, HTC do seem to have a nice one with the HD7. Given it's got a 4"+ screen, it's bound to be a talking point and though it's not currently Flash compatible YET (something Android is), it could well be a more media friendly phone. Just need to put up with the crappy MS points system they love to push. PC users though will probably enjoy the ease of integration with all their MS PC based software.
The Others
Symbian, which you've had experience of is on it's latest iteration on the new Nokia N8. It has a 12MP camera and looks pretty slick as well but I've heard it lags behind rivals on the software specs and in that respect feels rather dated compared to these new OS's. It does however have OVI Maps, which apparently in operation is a rather good alternative to a standalone satnav. The N8 also utilises DivX, which should in theory make it rather media friendly though the screen is no bigger than the iPhone's 3.5". Other aspects though like the web browsing leave a bit to be desired apparently.
Blackberry should be considered too as the new Torch is apparently a vast improvement over the previous Storm touchscreen models. My sis has one of the old school (a Curve if I remember right) and she seems to be happy with it. You get the usual array of apps for Facebook and such but they've apparently spruced up the OS a good deal and of course BB is one for being email friendly. The Torch also has the benefit of the pull-out keyboard, which is handy if you hate touchscreen text input. Things that let it down though are the old Nokia issue of slow processors and an overall lack of apps compared to rival OS'. From using my sister's, it seemed decent enough but I'm not sure if you'd have the range of software that Android/Apple have and WM7 will have.
I've kind of rambled on a bit as having issues sleeping, but given I'm vaguely in the same boat, I've been thinking about it a lot :laugh:
Some decent reviews
here.
then the replacement n96 lasted a matter of days before being crunched when I borrowed Stuartys vectra (don't ask!) 
