HTC E8 was released 8 months after Nexus 5 and is ahead in specs in everything.
For eg:
HTC E8 have expandable storage, N5 not.
HTC E8 have better processor than N5 and also a better battery.
E8 have better camera than N5.
BUT, if you consider prices of N5 16 GB, N5 32 GB and HTC E8, N5 16 GB seems to be more VFM at a difference of around 5.7K than other two models.
So it all comes down to:
1. Budget as in Value For Money (Best: N5 16 GB, if for you 12-13GB is enough)
2. Specs (Best: HTC E8 anyday)
3. Developer support and Coolness factor (Tie: Since Nexus is best known for Developer support (can run Ubuntu Touch), And HTC E8 is cool with those front speaker grill and Blinkfeed)
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Oh yea, but the successor of Nexus 5 in coming months can be a game changer.