i wud go 4 da nokia n73 tis da best! It's got lot of features on it and at the same time it's not complicated to use, plus on the whole there are more downloads, applications etc. available on nokia phones then there are on Sony Ericcsons! I've got one and its great especially if you fancy a bit of professional photography! But in the end the choice is yours!
I'd personally take note of what the consumer reviews say because alot of internet reviews are based on the product for one time only whilst consumer reviews might have what the phone is like to own 2-3 months down the line.
Also personally I wouldn't go with the specs that are given for a S.E phone.
I bought a Z530i which is supposed to have a decent camera, and yet the photo quality was poorer than my old Panasonic GD87 which only had a 0.3 MP camera.
My mate nick who fixes these things for his beer money says he sees loads of the K800is bought in for repair and he would go for the Nokia out of the 2. Apparently the K800i is very sensative to moisture, by that I dont mean when you accidently wash and tumble dry your phone, he means just general moisture in the air.