Tummy has 3 layers of tissues, skin, fat and muscle underneath. Liposuction is a fat removal procedure. Tummy tuck is a procedure that will correct the 3 layers skin, fat and muscle.
The liposuction is suitable if the fatty layers is significant, in this case, liposuction will remove what you can pinch from fat. Complications of liposuction are less than tummy tuck. Therefore if fat is the main concern liposuction will be better. However if there is loose skin that means skin will need tightening and removing fat unlikely to solve the problem and more likely to make it worse in this case tummy tuck will be better.

There is no guarantee of specific results and that the results can vary.