As someone who is a big fan of HTC and OnePlus devices, I'd say that's a difficult call to make. But I myself, given those choices, would potentially, most likely, lean towards the OnePlus 5T. Alert slider, still has double tap to wake, good camera (not that the U11 doesn't have that along with double tap to wake), and a great bang for your buck if you're looking to spare some cash.
Also, the fingerprint scanner placement could be your dealbreaker here. Do you like front-facing fingerprint scanners or rear-mounted ones? If you like picking up your phone and unlocking it as you are doing so, that's something to think about with regards to the OnePlus 5T. Or, if you like to leave your phone on a table or desk and like to unlock it while it's still situated "away from you," then the U11 has a good placement.
Also, not that I know this to a T (LOOL I didn't mean to be punny there, it just happened), but if you are one who likes to get regular updates, that may be something to consider against OP. The 5 doesn't seem to be in stock anymore and I have thought I had heard rumblings about previous iterations not always being supported. However, this could totally be misinformation on my part; so I apologize if I got my wires crossed there. Besides, most phones get updates and such for two years after their release date; and your phone can certainly run well without updates.
Anyway, please keep us updated on your situation! Also, the U11 is 5.5" and the OnePlus 5T is 6.0"; so if you're looking for a bigger or smaller phone, those are good things to keep in mind.
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