Cases are really a matter of preference. But to me I have a couple important standards; Fit, Look, and Protection.
Since the days of my 1st Treo 600, I have felt that protecting (physically) from my clumsy ways was the most important. For that reason I went with a Rhinoskin aircraft aluminum case. It was the best purchase I have ever made. I tried knock offs of the same type of case and the best fit, looks, and protection has been the Rhinoskin. Along with that though is a great warranty for 1 yr. My biggest complaint with my 1st Rhinoskin case was the clips. The clips are crap and I wore out 3 in a couple months. I called the company and the sent my 2 brand new and newly designed clips for nothing. I should note that the 1st replacement clip I used 3 years ago is the one I am still using. I have been using my current Rhinoskin for almost 2 years and it only now is starting to be in need of replacement. I need to replace it simply because I beat the crap out of it, it's scratched, worn, the padding inside slightly stretched out from my constant playing, and I have hit it so many times the clear plastic over the screen area is starting to push in.
If you are looking for a case that will REALLY protect your Treo Investment I have not found anything better than the Rhinoskin. At fist I thought 29.99 was a lot for just a case, not anymore soon I will go out and buy my 3rd and it's worth every penny. Good Luck.