Both are great phones but here are my reasons why I stuck with the Z10
1. Better design- bezel, buttons, more stealth looking in all black, lighter more compact. Z30 looks generic.
2. Brighter and sharper screen
3. Back cover of the Z10 feels better than the weave design of Z30
4. Removable battery
5. About $200 cheaper for basically the same OS, performance and specs