My advice would be to look at which ADW's are available in your state, and then find the one whose promotions/rewards fit your style of play the best. I'm a small player, so I like the cash-back-for-2d-or-3d promotions, but that wouldn't appeal to those whose bet size is larger than mine. If you play a lot of NYRA races, NYRA Bets has the most promotions for those races. If you play a lot of multi-race exotics, many ADW's feature hit-and-split promotions. And, of course, if your play is large enough, then rebates enter the picture.

DRF Bets is an odd duck, because it cannot take bets on CDI tracks, but I like the bet pad that has projected odds and recent Beyers.