I really, really wanted to like the HTC One - but there are a few things that put me off it:
1. No Removable Battery/SD Card. I don't use the battery switching a whole lot on my GS3, but the SD Card is invaluable.
2. While I like the general design - I can't stand the huge speaker grills on the top and bottom of the display.
3. HTC is notorious for poor battery life.
4. While I'm not a huge modder, I do like flashing the occasional ROM here and there - HTC phones are a pain in the ass to unlock and get ready for rooting.
5. I've dropped my S3 a few times, and the back has gone flying off, which sounds horrifying, but it absorbs the shock and doesn't damage the chassis. I can't imagine an aluminium body would resist damage as much.
6. This could change once proper testing happens - but im not 100% sold on the Ultrapixel camera.
EDIT:
7. I love the new camera features in the S4.