Finally made a decision (only 5 months beyond contract expiry) and after an hour in the EE store yesterday comparing the 2, I bought a Galaxy S4 over the One. That ends my >10 year relationship with HTC phones. Or would, if they'd actually get round to transferring my number, so my Desire HD soldiers on till they finally switch!
It was the lack of a memory card slot or 64gb option that turned out to be the crunch for me, but it wasn't helped by the double data allowance on the S4 on 4G (despite not living in a 4G area.... silly, but apparently still cheaper than it would have been on 3G) and better discount over the One, and perhaps the potential to use with my Samsung Smart TV. The One still looked awesome and was less gimmicky than the S4 but I couldn't get past 32Gb hard limit, and the fact I've filled my 32Gb micro SD on my DHD. No card slot seems like a backward step by HTC and one I was hoping they would have reversed with the One.
I'm still not entirely sure I made the right decision though! I guess I've got a week to decide.... 2 annoyances at the moment are the headphone socket on top (dunno where it was on the One??) and the warnings that keep coming up telling you to avoid using it when charging when my battery is about to die (and the warning in the book telling you NOT to use it during charging or else risk electrocution. seriously?!?!). I mean surely I can still use the thing plugged in????
Anyway, those are probably questions for the S4 forum, which I'd better start looking at!!!
Bit sad really