@RushW I think you play on PC, right? i play on Xbox and I simply have to press A and then either Y, B or X against the first opponent (the second and third opponent are like AX AX AX AB AB and something like that). The Valentine one is easy because you don't need to be that fast and the first opponent often fails a few times. Just beat the first opponent, then leave as soon as the second one comes and rest some hours in the hotel and when you return it should be the Level 1 opponent again! But I don't know which buttons you need to press on PC and if the first round is as easy as on Xbox...
But there will be another Gambler Challenge where you need to win a round of FFF in every location! And trust me, Van Horn and Strawberry is TOUGH! You only need to press two buttons (on Xbox) but in Van Horn you need to complete as many rounds as possible before you stab your finger and if you fail once, the round is over. In Strawberry you have twenty seconds to complete as many rounds as possible (depends on the opponent! Sometimes easy sometimes tough).
So all in all I can recommend Valentine for easy FFF wins but you have to win one round in every location in another Gambler challenge.