Personally I don't care much for the Sony software, I'm using PA 4.4 and I'm quite happy with it, and any other phone I get will probably end up being the same.
What it really depends on is if they make a phone with everything I want in terms of hardware, currently what comes closest is the Oppo Find 7, if that was 5" it'd be perfect, but alas there's the trend to make phones bigger...
I'm pretty happy with my ZL so I'll probably end up waiting another year at least before getting a new phone.
Current: Xperia ZL C6506 + PA 4.4
Previous: Galaxy Exhibit II 4G w/ CM11