I've had the hard plastic cases on other phones in the past. Over time, from the phone slightly shifting around in them, they can cause very fine scratches on the phone itself. Just something to think about if you care about that sort of thing.
More proof of the hard case scratches here.
And the hard rubberized case, is just a hard plastic case with a very thin layer of silicone rubber over the exterior of it. After a few months, the thin rubber coating tends to wear away at the corners.
From that experience, I went with an actual rubber case for my Ascend. The brand is Amzer. It is solid rubber, and offers more grip to help keep from dropping the phone by accident. The corners are also thicker to help protect it in the event that you do actually drop it. It does not cover the Cricket logo though.
Here's an example of one I am talking about.
Amzer Silicone Skin Jelly Case Huawei Ascend M860 Black - eBay (item 120692048747 end time Mar-31-11 13:30:32 PDT)
I found mine on eBay for 99 cents with $3.00 shipping, so shop around. You can get them in other colors.