I hate answering this question but its really in this order (spoken as a reviewer and only in terms of the feel of the keyboard - not the OS, 3rd party software, etc.):

- Blackberry Curve
- Blackberry 8900
- any Palm Treo
- Nokia E71/E63
- Samsung QWERTYs (really, they are all the same)
- pretty much anything else (because really, they are horrible unless I've named 'em)