Round 1) Gambit, better and more experienced fighter
Round 2) Ant-Man thanks to his powers
Bonus) Gambit is a former Thieves Guild's leader who has been trained to be a thief since childhood, without powers it's not even a competition. However Scott's powers even the odds and probably give him the edge between size alteration and a whole army of potential helpers
1: Gambit's shown much better hand-to-hand prowess so this round goes to him.
2: Ant-Man. I don't think even Gambit's aim is good enought hit Ant-Man at small size & if Scott goes giant, he easily outmatches Gambit.
3: Tough, but with a suit that lets you literally walk through a crack in the wall, I'm Team Ant-Man.
Round one: gambit was able to best wolverine in hand to hand. Scott is unlikely to win. Gambit wins.
Round two: difficult fight, but gambit can charge cards and surfaces. He's proven to be a top notch marksmen. Hes also pretty impeccable with timing explosives. Even if he doesnt directly hit him he can get him with a few blasts. I think gambit wins with difficulty.
Bonus: gambit is more experienced and has a natural talent for thievery.
Also, for people questioning gambits accuracy, heres a panel in which he cuts a wire 1 millimeter thick from 50 feet away to prevent a nuclear device from going off, preventing its explosion before the trigger person can hit the button.