Hmm, they're almost similar of you don't mind the Xiaomi skin...o personally preferr OOS over all other OEM skins except for the stock on pixel devices .
Also I think development wise OnePlus proved to bwore versatile still, xiaomi released the Poco specially to compete in this space and still not on the same level as OnePlus (in my opinion) ...
So in short I think for dev purposes , you may go for the 6T
Dont mind skin as I will change it to something closter to stock android . Tbh recently moved to oxygen ( for all years with one plus since mk1 i have used oxygen for 5-6 months ) i think i fancy a challenge (mi8) but love OnePlus for its dev community . But other hand mi dev just get better and better and develop to the point where OnePlus is now.
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