Personally I would by the Xbox One, I have a PS3 and will be the new PS5 if it ever gets released just because I own it since the PS one and love the remote.
Anyway the reason I say buy the Xbox over the switch is because it will end up in your living room as the home entertainment system with netflix and 4k streaming. Dad and his new toy (disguised as a gift for the boys)
The Nintendo switch is like a upgraded version of the PlayStation Vita, which was nice at the time, but you have mobile phones now packing more detail. If I was you, I would go to Cash Crusaders and buy a Xbox One plus 2 controllers plus a ton of games all for less than what the Switch would cost new.
I don't think I would've been able to tell the difference between new and used when I was 8 years old.
(Being a financial focused forum, I had to include the "don't buy new at inflated prices" comment.)