A lot of variables here. The biceps have a pretty limited action list, so it's easier to say something like chin ups and barbell curls are some of the best movements for them. With the "abs" it's not so clear cut and dry. First, "abs" usually means all 4 muscle groups of the rectus abdominis, transverse abdominis, and the internal and external obliques. They all have different functions and I'm not aware of any worthwhile exercise that recruits ALL of them in a meaningful way, maybe some circus trick exercise that isn't even worth doing. So there's that, and then take into consideration that when you open a body up, there is no distinction between front and back. The "ab" muscles wrap all the way around the torso (except the rectus), SO if you want strong abs, you also have to have a strong back! Now, Dr Stu McGill has pretty good info out there that Abs are really reactionary muscles, they exist mainly to resist torsion in the torso which means that when you do exercises to strengthen the abs you have to include isometrics and eccentrics. So not only can you not pick an exercise that BEST trains the "abs", you also cannot just do CONCENTRIC exercises either. However, with this info you now have a good idea on where to start when designing programs aimed at strengthening your abs. ***Bonus caveat - train them the way you plan to use them. Like grip muscles, "ab" strength is very relative to the motions and actions you train them in. Hope that helps