I have been using IAS for a couple of years now and find them to be the easiest to navigate they give decent prices (atleast better than 2 of the TABs some times all 3) they have exotic betting (quinella, exacta, trifecta, 1st 4) they also put up promotions every now and then which could get you the odd free bet although there are conditions involved with the free bets also, another thing I have found interesting is that they also have a feature i think called protest plus in which if you have backed a horse which crosses the line in 1st position and it loses the race on protest they will pay out anyway upto $1000.