A standard anchor for many sport climbing areas is for the leader to just clip two standard quick draws to the bolts and lower off. This is certainly safe enough in most situations, and the fact that it is been done literally millions of times without incident should probably tell you that it's an acceptable practice.
Having said that, there’s some cases where having two designated quick draws with locking carabiners on each end can be a Good Idea. If you’re in an instructional setting, with many people top roping off the same “unattended” anchor all day, without a more experienced person going up regularly to check things, locking carabiners can add great peace of mind. Because it's a top rope, you’re not right there next to the anchor to see if any carabiners are getting cross loaded, gates getting unscrewed, or other strangeness that could lead to an anchor being compromised.
Personally, I have two designated quickdraws just for anchor building. They are the Petzl Express 25 cm long draws, the longest they make, and four locking carabiners. Each pair of carabiners is distinct, so I know which is for the rope and which is for the bolt. The longer 25 cm draw gives a nice narrow angle on the anchor if the bolts happen to be a bit far apart.
This is an easy and inexpensive set up. You probably already have a few extra locking carabiners around, and the long “dog bones” draws are only $5-$6 apiece.
If you’re inclined to be a little more cautious, using lockers on your sport anchors can be a little extra insurance, with low cost and high confidence factor. Look at it this way: Other climbers might call you a little paranoid, but there's really not much downside to doing this.
Two standard quickdraws with non-locking carabiners. Bottom gates opposed and opposed. Nothing wrong with this setup.
Here’s an alternative. Similar setup, this time with 4 lockers.
Which anchor would give you more confidence?