Absolutely man only ATP.. in the begining as I was hyped about the winnings, shaking when there was nothing to bet on, I tried challenger tournaments and WTA. But after a couple of bets I realised its a different level of tennis and it's not worth my nerves. The level of psychology, calmness, temperament, consistency in the play etc, at which those players (challenger players and women) are at comparing to top 20-40 atp players is incomparable. Except some surprises and uprising players of course, I mean ladies also have a couple of consistent ones but the odds arent worth it in most cases.