One of the very most common questions I receive: how/whether to compare your book to another book or books in the query.
I personally don’t mind at all if you compare your book to another book or author or two to put me in the right frame of mind. This is completely optional, so don’t feel as if you have to, and honestly I’d just use your best judgment about whether you think it would be helpful.
The only thing I would suggest is that you don’t compare your book to 1) a megabestseller or 2) something extremely obscure.
1) We agents get zillions of queries that declare themselves to be the next DA VINCI TWLIGHT POTTER SECRET, and trust me, you don’t want to be in the company of those queries. Honestly, people, what megabestseller is anything like the last megabestseller?
2) If the reference is too obscure you are risking that the agent is going to be all, “Dear god man, I haven’t read everything.”
At the same time, the right mix can indeed put an agent in the right mindset. So compare away! If you like.