Where can I find the best bitcoin betting sites?

In this list of course. But jokes aside, a quick google search and a bit of research can also provide you with an extensive list of options.

Bitcoin Casinos
SapphireBet Casino
SapphireBet Casino

100% and 30 free spins up to €300.

SlotVibe Casino
SlotVibe Casino

100% up to €200 or 1 BTC + 150 FS (5x30)

CryptoThrills
CryptoThrills

70 no deposit spins + 250% bonus up to 1 BTC

CasinoBTC
CasinoBTC

Welcome bonus up to 5 BTC