Official one is great, and I use it for non work applications.
However, they seem a bit pointless, as they cover only the virtually indestructable back cover and just really dress the phone.
Amazon hard rubber one is my favourite so far. Thats my work one.
Surely the rubber one only covers the back too? yet it's bulkier? No cover protects the screen in reality when dropped unless it's one of those that has a flip over the front. I had a Gel one on my desire that wrapped around it very well and I still scratched the screen after a drop onto tarmac, luckily I had a screen protector on, which I also have on my OX.