The NEC and Siemens have the smallest displays so the amount of useful information they can display at one time is obviously limited. Web surfing with such small displays would frustrate most users -- even the bigger displays are a tight squeeze.
The Blackberry and Treo are a step up in size, and both displays are crisp and sharp with the Treo easily the best. None of the phones were bad and all the screens were bright and given their relative sizes, and remarkably sharp.
The Sony and Motorola displays are slightly smaller than the O2 and i-mate. The latter are a joy to use -- large, bright, and very sharp.
The Nokia is a strange beast -- its landscape display is very wide but not particularly tall. It is, however, colourful and sharp, 640 x 200 pixels sharp, and can display surprisingly large chunks of data.
Camera
The digital camera is fast becoming a given for mobile phones. Only the Blackberry, Siemens, and Nokia did not include one.
Low-resolution cameras are fitted to the O2, Sony, and Treo (which has a 0.3 mega-pixel VGA resolution camera). The i-mate has an in-built flash unit while, interestingly, the Sony has infra-red night mode -- much like their consumer video camera range.
The remainder of the cameras are around the 1.3 megapixel range -- only the NEC features a flash unit. The Motorola and O2 make do without.
Although it is not quite available yet, you must also check out the next HP iPAQ 6500 - it is the size of a Blackberry 7230, but so much more capable; quad-band phone with EDGE, 1.3Mpix camera & LED flash, Bluetooth (no WiFi), GPS!!!!, and the usual PPC2003SE stuff (hopefully upgradeable to WindowsMobile5.0 in Oct or so).
http://www.brighthand.com/article/iPAQ_hw6500_Coming_in_September?site=SmartPhone
http://davesipaq.com/news/ipaq_hw6500_comparison.html
And here is a link to some recent forum comment about the size (smaller than a normal iPAQ), battery life (better than a normal iPAQ, not as good as a Blackberry!) and built in keyboard (very similar to Blackberry).
http://davesipaq.com/forum/showthread.php?p=35358#post35358
It is already released in Germany & UK (in theory at least!) and I'm hoping to see it in Australia in Aug or Sept..