well you are talking about three phones that specialize in different fields here~
N80: (Smart phone)
- does considerably acceptable picture quality (downside being the fix focus which affect practicality)
- great UI, symbian OS. it is slow but very flexible and fun to play with
- major feature being wifi, great browser, very conveneint
- slider, personal preference style wise
N91: (Smart phone)
- don't look at the camera, it's not the hype's here, nokia didn't design this phone to give you photo quality
- major feature being the micro drive, imagine using four gigs of hard drive, you gotta ask yourself do you need that much.
- again, symbian OS
A1200: (Smart Phone hybrid pda thingy)
- don't worry about the camera here, it's not a camera phone, altho it's 2.0 megapixel, the no flash and no auto focus makes the camera very impractical here. you will get some quality pictures in day time under strong sun, but that's all
- great UI, Linux with a stylus, you can really use it as a pda~
W810i (camera phone):
well, it's just not the same thing, you are comparing apple and oranges here, this phone has the most practical camera here imo, it has autofocus, great flash, and good photo quality. but it's not a smart phone and it will not does thing like a smart phone.
you really have to ask yourself, which is a key feature to you? if you said none of the things are important, then really, just go with the one you like the style the most~