Cost isn't the biggest factor, just part of the overall equation. You do bring up the two biggest factors. The phones are close, so I should be better off with One, given the price difference. However, staying power is also a concern, as my 2 year old Bionic limping along demonstrates. Looks wise, the One is, imho, the sharpest phone available, if not ever. That would fall more under the tie breaker category, however.
I just need to find a store that has both working models on display so I can do a side by side.