What's the best lower ab exercise?

Answer 1

Hanging knee raises.

Don't let anyone tell you leg lifts. Leg lifts work the hip flexors.

Answer 2

That is a very difficult question to answer.
You know the saying "variety is the spice of life" or "everything in moderation"? You actually want to vary all your ab exercises.
If you do a curl to target your bicep, your forearm still will be working because you have to hold the weight in your hand. So by that theroy, even if you do target specific upper ab or obliques excersise you are still indirectly working the lower abs. Just on a much smaller scale.
Okay I might be going on too much here, making a simple question over complicated. Any type of leg lift work will suffice. Straight leg or bent leg or others that at this moment I cannot remember.
Just make sure you vary the different types, that way you should get faster results. Good Luck.

Answer 3

Knee to elbow
lie down and cycle without bike
and another one where you look like a whale (but I can't tell you the name of it

Answer 4

lying knee raise and captains chair. Romanian deadlifts are also effective

Answer 5

knee lifts