Raichu > Pikachu
Pikachu is all Speed and Sp.Atk, the rest of its stats are so low that any attack, effective or not could KO it. So it cannot survive and attack if it doesn't OHKO its opponent.
Volt Tackle, not really such a good move. Unlike Double Edge which isn't super effective against anything, Volt Tackle is, which means it can backfire by doing even more damage to yourself if it does x4 damage to a Pokemon (Gyarados), or if you get a lucky critical hit.
Unlike Raichu, Pikachu is incapable of ''sweeping". Plain and simple, its only special attacks would be electric based and Hidden Power. Raichu has a strong enough attack power to do some damage with a Focus Punch, Pikachu couldn't even do 1/4 to Tyranitar, which has a x4 Fight weakness...