I used Coinbase a couple times in the last couple months and it was a huge hassle. You have to wait about a week for the btc to show up in your account. Not only that but they lock you in at the btc price for a week and you are subject to whatever fluctuations there are. On one of my deposits I lost $300 because of fluctuations.
Today I used itbit for the third time and it works much better. You have to physically wire the funds from your bank which is the only downside. Here is how it worked for me today:
10am: wire $8,000 usd from my bank account to itbit.
1230pm: got an email from itbit letting me know the funds were ready for use.
1240pm: Buy btc with my usd.
1250pm: transfer btc to poloniex (or blockchain or whatever your intermediary wallet is).
Now I can just deposit the btc into whatever sportsbook I want.
In one day I will move $8,000 from my bank account to my sportsbook using itbit.
It would have taken at least a week with coinbase and I would have been subject to btc fluctuations.