UU is the tier for using mons you love without the over-centralization of OU. UU has some awesome mons in it that can't quite handle OU, but are still excellent.
The current ORAS UU is the closest thing we have now to the delight that was DPPt OU, in my opinion. Not too many megas either, and the ones that exist fit in nicely without being too borked.
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