My Chimchar i've had in PKM Diamond since I was like 5, was called Smokey, and he's now LVL 100 DESTROYER OF WORLDS, and he's called Smokey. Brilliant.
i named my Sableye Gemini (gem-in-eye)
also, i alwaaaays name my starter pokemon in spanish. i named Fennekin Zorro (fox) and my Rowlet Almendra (almond)
i named Pichu Meteor. i really don't know why, it just popped into my head when i saw it. but i think its just adorable
My double battle lead Pok?mon Reuniclus and Bronzong are called 'Herp' and 'Derp'. Following this naming convention, their teampartners Tyranitar and Garchomp are called 'Hurr' and 'Durr'
This is probably going to be a matter of opinion on whether they're the "best nicknames", but I called my alolan exeguttor lord+saviour. All written together I think. I also called my alolan raichu Hank, as a suggestion from my friend and I think it's hilarious. Not the most unique nickname, but it reminds me of good times and I always get some kind of comment from people whenever I tell them what my alolan raichu is called.