I've always been lead to believe that included in your covering/query letter to Agents, should be reference to other authors who you compare your writing to. But I've just read on an agents submissions page that this should not be done, and rather let the agent think for themselves. Any pointers on this?
Comparing your work to other authors: No.
Giving a contextual reference point to your work: Yes (my novel is Gone With The Wind meets Jaws, in space)
Placing your work in the existing market: Yes (my work will appeal to fans of Dan Rhodes and Sue Townsend).
However, it's a bad idea to overstretch on these - Dan Brown, J.K. Rowling etc are not great comparators.
I've found that there's generally mixed advice on this depending on where you look. Personally, I prefer to submit my work and let the agent make up their own mind about it. That way it can stand or fall on its own merit, not because of possibly unrealistically raised expectations on behalf of the agent who is doing the reading.
I would never refer my work to someone else when approaching an agent. Once you have told them your work is as good as JK Rowling or J. R. R. Tolkien you open the trap door.
If they don't ask don't say. Let your voice do the talking.