What's the best way to lose my gut?

Fast vs best: Liposuction is the fastest way to get the fat off the waistline, but not practical. Gastric bypass is probably standing at second, but again not practical. So, i would recommend starting with calories restriction along with good amount of aerobic, ab crunches, and weight bearing exercises. Kick-boxing is incredibly effective, but tough to do. Swimming can be added. Consult your doc. Good luck.

Gut: There is no such thing as spot fat loss. You would need to lose weight in general & a certain proportion of that will be abdominal fat. This can be done by eating healthfully, being physically active and making sure that calories burned exceed calories consumed. However you can improve your appearance by toning your abs. To tighten your abdominal muscles consider doing crunches, reverse crunches.