Make a list of all the pros and cons for each device and then forget it for a couple of days; don't even look at it. Come back to the list and see what jumps out at you. You'll find your thoughts wandering towards the device you want over that time too.
If cost is a major issue, like you seem to say it is, then I would go for the cheaper device.
To be honest, I have an HTC One and I can guarantee you that in two years it will still be running the latest apps. The reason I say this is because I have a Galaxy S2 that is still doing fine on that front, well over two years later. App makers don't want to do themselves out of revenue by only
catering to the latest and greatest devices. Don't worry about that.
The other thing you could do, and bear with me here as this sounds silly, is to flip a coin. Make sure you name one device heads and one tails and I bet that when the coin is in the air, you'll know exactly which side you want it to come down on.
The HTC is a fantastic device and the build quality is great. However, I put mine in a case so the lovely Aluminium back isn't being shown to its fullest extent. My Note 3 (replacing my SGS2) will also be in a case too, so I think that is a moot point for me.
I hope this helps.