I have a Z1C and Z1.
The Z1C has an IPS display and has far superior viewing angles, colour and contrast to the Z1 (I also have a Z2 and it's display image quality is on par if not a touch better than the Z1C).
The Z1C is a lower resolution display, but due to its smaller size, the dot pitch is almost the same as the Z1. However, content such as web pages is more cramped and harder to read on the Z1C.
It really comes down to how you use the device. There are some days where I love the size of the Z1C, and others where it frustrates me.
I have relatively skinny fingers, but I still struggle to type on the keyboard on the Z1C as the buttons are quite small, but it's no worse than on an iPhone and I'm sure I'd get used to it after a while.
I don't really think one is better than the other as ultimately it will come down to which suits your individual needs the best.
Be sure to check out our new/free Android game - Can you be the Wheelie King?