Erm... those are very broad questions that make me think it'll probably be -EV for you to be betting on sports. But since you asked...
If you're able to from your country of residence, then Pinnacle is one of the best choices as they offer the highest limits, lowest vig and don't limit winners.
You might also want to look into promos or special offers with any local sportsbooks you have access to, as you can often arb them for free money. That'll get you banned or limited at most of them but still, free money.