Hi I am more or less in the same boat as you. I have the Z3C and the Z3Tab.
Battery life has been great on the phone and for my usage, I get 1.5 days of use which is really good for me. I mostly use my Z3Tab for game, video and browsing while at home but once in awhile I leech data off my phone if I need to load stuff while on the move. During those times, my phone will have 20% at the end of the day.
I leave the phone on LTE practically all the time when im not on wifi. But Starhub hasn't got the best 4g coverage so there are times it will switch to 3g. Voice clarity is good especially during the times its on 4g. The screen is really lovely to look at, if ur not that particular about resolutio. The colour reproduction is really pleasing to the eye and I prefer mine wwith the screen gimmicks turned off. It can go real bright and also dim enough to use in bed.
What I really like about my Z3C is the size. It's very pocketable, light and having a tablet around, the size complements each other