Sony Ericsson phones have excellent build quality, GUI is rather good to.
Almost as good as Nokia
Nokia's build has dipped latley but back on track now with the very latest phones.
Nokia 6300 is an example of Nokia back to form, avoid Motorola phones, just plain awful! Their GUI has not been updated since the £1 note was in circulation.
N95 is a cracking phone, N95 8Gb is a nice update, and buid quality is up too.
We have some iPhones at work, fantanstic consumer device, but has some serious flaws:
Does not support wap pushes
no mms support, so no picture messaging
camera is appauling
no 3g capabilties.
The screen is cracking though! really amazing stuff.
Nokia - used to be my personal favourite, imho, went off the boil a few years ago. Their styling was out of date when everyone wanted flip phones for some daft reason. They seemed to have been playing catch up ever since. In particular, from a laymans point of view, they have never truely got to grips with Symbian.
The N95 was released long before it was ready. Only now is it stable enough, but it should be approaching EOF now. And I find the latest software for it unusable - its horrible, bland, not user friendly.
I think the iPhone wins in terms of user friendliness, with Windows devices (proper touchscreen) a close 2nd. For power and apps, Windows wins hands down thanks to the fantastic tools available via .NET. Neither are much cop for 1 handed texting, but I find the Windows devices the easiest for texting (2 hands), but thats probably and age thing
As a PIM, Windows probably syncs better than anything, though for syncing over-the-air it works best with an Exchange server.
As a Satnav, Windows runs TomTom better than Symbian due to the touchscreen.
If I was getting a new phone now, it would either be a Windows device, or a really simple no frills Nokia (the Symbian Nokias are just too unstable - even compared to the Windows devices!)