there’s no single site that ALWAYS has the best odds it varies by sport and event. But from my experience, bet365 consistently offers competitive odds across most sports, especially for football. Their odds payout percentage is around 93.47% which is pretty solid. For tennis specifically, they’re both highly rated with good bonus offers and extensive coverage. If you’re looking for value, I’d suggest checking FanDuel and DraftKings too they’re both highly rated in the US market.