Both of these tokens have done wonders.
BTC is the opening coin for the idea of blockchain & crypto revolution. Currently, Bitcoin is still the leader of this revolution.
YFI is a token of a project to mine liquidity pools for DEXs, it also leads the DeFi wave to help the entire crypto market survive winter 2018-2019. This helps to perfect the DeFi ecosystem, which is surprising given the limited supply, 1 YFI = S45K in the past.
I prefer BTC because it's simple: KING is unique.