I like to do grounded up-b when are near the ledge, it will push them off the edge and get hit by part of the up-b. Also it is used for awesome pressure.
Down b, is best used against people who rely on their ground game, snake, ic's, diddy, DDD, and others. Also use it to tech chase, little known fact, you can down b on a platform (not smashville) and it will hit most chars that are stading below you.
Against Pika, bairs can work, you can bair threw a jolt and hit him in the face, or you can run right under the jolt and get a free grab, it just depends on where you are and what the pike is doing.