Personally I would go for the cheaper option however if you spend a lot of time gaming and don't really care about fine pixel detail from your photos get the One M8, never the less games will run on the 830 however you will only notice the difference if you compare them side by side.
Also if you pick up the 830 you do have the option of MixRadio which is I feel is greatly superior & more polished than the xbox music app. Furthermore the mixradio sub is also cheaper than the xbox music pass, however there is no MixRadio app on the xbox one and you need a sub for mixradio to get the full experience on Windows 8.x+ (the same will go for xbox music as well come December 2014, no more free music streaming). As your in the US you do have other decent alternatives, i.e pandora, spotify. (The other bonus for MixRadio is that it is completely ad-free

)
Furthermore the 830 has perks the One M8 doesn't namely wireless charging, there were countless times where I used to fumble in the dark looking for my charging cable whereas now I can just drop it on my charging plate. Sure it is slower but as most people put their phone on charge before going to sleep and if you barely use your phone during the day then the difference in charge times will be hardly noticeable (since your going to be in a comatose state for several hours :P) .
Additionally, with the Lumia 830 you are essentially guaranteed support as the support will becoming directly from Microsoft where as with HTC.... they have been rather absent for their previous devices (same with Samsung). Hopefully this changes with One M8 but I'm not holding my breath.. given the store reps disdain for anything windows phone, which is really going to hamper One M8 sales compared to it's android variant.