Coinmetro, because it's easy to buy QNT there, low fees, and they are eu-regulated
Honestly I never heard of this exchange, it's just a small exchange, right?
As I check, they only have over $120k trading volume as of now, very low compared to the big exchanges in the market where they have at least $100 million on a daily basis.. (
https://coinmarketcap.com/exchanges/coinmetro/)..
I guess everyone would choose the top 3 exchanges in the market, as for me, it's always been Binance every since.