Offshore sites are the best for placing your bets at the moment. I chose 5dimes because of the variety of sports you can play and they have the best lines. During the NFL season you will notice a difference between Bovada and 5dimes, where 5dimes will have lines early on Monday for the next NFL week, Bovada(The US approved betting site) are very late to post lines, and are most unfavorable.
Keep in mind, there is no word on parlay bets. Single bets are now allowed if the states approve. I think DraftKings and other fantasy sports places will have this option to bet on a single game soon.
If you want to bet parlays, go with 5dimes.