Let's suppose we have two bolts which are connected with a chain and a ring for rappelling at the top of a climbing route and we would like to install a top rope setup.

I hear on a monthly basis that two quickdraws facing opposite sides are unsafe and I should use instead one locking carabiner.

What is the preferred way to do it? Putting the rope through two quickdraws or one locking carabiner?

Ps. For reasons of wear I would like not to use the ring directly and use instead quickdraws or a locking carabiner.