Update:
Choosing a case I like is proving more difficult than choosing the phone was!
Anyway, I'm very impressed with the Xperia Z3 Compact. Works quickly and smoothly regardless of whatever I do with it. A single battery charge lasts a whole day of intensive use (while I'm learning and trying apps like mad), so hopefully it'll still have enough capacity for typical use when it's half dead in x year's time - which is fortunate as the battery is not user-replaceable. (It's bound to be physically possible to change the battery, but probably with risk of damage). I do badly miss the BlackBerry's physical keyboard and trackpad, but I expected to.
Regarding app storage on this phone: some can be partially transferred to the Micro SD card, but not fully, and some apps not at all. Perhaps this will change when it eventually gets Marshmallow. (Android's release notes imply so). There's room in the main memory for plenty of apps, meanwhile.
Also, some unwanted pre-supplied apps can't be uninstalled, although I've worked out a trick to save them taking so much memory: Delete their "data" and uninstall updates to revert to "factory" versions (which tend to be a lot smaller), and disable them and don't update them. I don't think I'll get into rooting.
