Mobile phones are getting worse, and increasingly less "mobile". The best mobile phone I've ever owned (and still own) is a Panasonic A100. Less is more.
Nokia 5210. This mobile phone is a very long time, obviously not including the smartphone category, but I really like the toughness of its hardware
I know a lot is down to personal preference but the best phone I've had is the iPhone 4. I don't think it is really the phone itself that is so great rather the apps and the way you can just install new apps to get it to do new things. Having said that Android also have apps so if I'd bought an android phone I would most probably say the same about that. I did have a Blackberry which I did not think much of the available apps but I totally loved the qwerty keyboard.
My best is the mobile that I own now, which is a Sony Xperia Arc. I can download apk and install all the apps I want, which is great!