Only one comp title?

If you can compare your novel to something more recent, then I would go for that instead of something older and famous like Alice in Wonderland, Lord of the Rings, Harry Potter etc. It shows you are aware of the current market, and the trends and cliches involved (meaning your manuscript is less likely to have fallen into retreading old and tired territory).
In my experience they tend to prefer three comp titles but if that is the best fit, then it's the best fit.

It should be more of a sales comparison than a thematic comparison to your plot/story, e.g., if you are a first-time novelist with a fantasy novel that is the first of a trilogy, find successful books that are similar to that. Also the comps should be no more than two or three years old.

What Cameron said. If it helps, I didn't have comp titles in my query letters and I still received requests for fulls. Instead, I said something along the lines of 'my book will appeal to people who enjoy So-and-so's voice', and 'my novel would sit comfortably next to books such as X and Y.'

HTH

While more recent comps may show the agent you’re well-read and up-to-date with the genre, if your perfect comp title is an old one, go for it. Just be sure to indicate *why* it’s a relevant comp, not just plunk the title there with no reason.

For my query, one of my comps is a decade old (or more?), but I reference a specific aspect of it that relates to my book. I’ve had manuscript requests and an agent outright complimenting my query, so I think it must be working somehow, hah!

Of all the things we writers stress over this shouldn't be one of them. It's as Cameron and Super_Duper said: the request for comps assures the agent that you're aware of your market and what that agent represents. It also lets them quickly ascertain whether they know any editors looking for works like yours. It's a sort of shorthand for all that—and really that simple.

I don't think I had any comp titles in my query last year. But it still got a lot of attention.

I love this blog post by literary agent Laura Zats on competitive titles vs comparison titles--you might find it useful: https://redsofaliterary.com/2017/07/21/notes-from-the-armchair-the-curious-case-of-the-comp-title/

For a competitive title, it should indeed be recent, but I see no reason why you couldn't use just one: "The humor, historical setting, and speculative thread of [my novel] will appeal to fans of THE GENTLEMAN'S GUIDE TO VICE AND VIRTUE."

For a comparison title, one is also fine, and it can be from any period, if you have a clear and interesting twist. Aliens was pitched as "Jaws, but in space." If your novel is about a girl who falls down into a fantasy land--only it's from the perspective of someone who lived in that fantasy land already and liked it just fine before the brat dropped in--you could call it "Like Alice's Adventures in Wonderland--if it were told from the perspective of the Red Queen." Make sense?

Like others have said, comp titles are nice, but not essential, so don't agonize over it if it doesn't seem to be working for your particular project.

Late to the party, but I've never had comp titles in my queries, and I got 2 successive agents from those queries. They're good shorthand in Twitter pitches though, and they don't all have to be books.