Actually, if you still haven't bought the phone yet, which I assume you already have made your decision, but regardless: I would highly recommend the new LG G3. It has an amazing 2560x1440 screen, which is higher resolution than most home PC's on a ~5 inch screen, which makes for some amazing viewing(all of this and following from MKBHD and other reviewers)! It also has a host of good software, and despite having such a high resolution, the phone doesn't ever really lag whatsoever. It also has a really good camera and cool features such as laser auto-focus and many more, plus a really good battery that not only is roughly as good as the very strong one inside the HTC One M8, but is also removable.
Honestly, I really like my HTC One M8, a lot, but if I were presented with the choice between the M8 and the G3 right now (the G3 was not released when I purchased my phone), I would probably go with the G3.
The only big issue with the G3 is that it is easily overheated, so much so that you will have to limit your screen brightness because that can make the device get too hot and give you an on-screen warning about it. Also, speaker quality is meh, nothing near the HTC One M8.