Depends on your goals, homie. Consider the primary function of the rectus abdominus: static holds – bracing.
Squats and deadlifts are great for your abs because they use the abs for what your abs are meant to do. Full flexion of the spine is generally a shitty position to be in, and when you are in it, it's not likely that you're going to be fighting anterior resistance. You'll ideally only flex your spine if you need to carry an atlas-stone-like object, in which case your rectus abdominus doesn't do shit except assist in the initial spinal flexion, and then BRACE in that position.
But I mean if you want to feel good that you "trained abs" today, that's cool.