HTC One looks great and got great build quality. I don't care about lack of SD cards, because 32 / 64 gb is more than enough. My only concern is software - Sense is heavy, HTC isn't very fast at updates, locked bootloader and lack of sources.
I currently have SGS3 and 4.2.1 leaked a few days ago, so it got almost lastest software (and newer than HTC One currently). In less than 3 months Android 5.0 will be revealed and then all those flagships will wait some time to get it. So despite I really like HTC One, Im thinking to keep SGS3 for another few months (especially now when Im running 4.2.1 on it) and get X Phone with Android 5.0 as soon as it is available. If HTC One would have good support for AOSP (like for example Sony), I would get it for sure. Also if I would have some older phone and I would need to buy something, I would choose HTC One.