LB to strip, RB to cover.
Both work, but in the right situations and at a pretty realistic rate.
Most guys don't know about covering up in traffic or just forget, so they leave themselves open to the strip. Covering up definitely works to minimize fumbles and is necessary in traffic.
To Val's question, you can move the pile with the R-stick while covering up, and even can break a tackle that way if you have a strong runner. But you're most often limited to short pushes of the pile, as you should be if most of your energy is concentrated on protecting the ball.