A comparable is not your favourite film. It is a produced film that answers three questions for a buyer: who watches this, roughly what does it cost, and who has already made money doing it. Comps are how a stranger decides whether your script is a business or a hobby.
Pick recent and honest. A comp from thirty years ago tells a producer nothing about today's market, and comping to the highest-grossing film in your genre reads as inexperience. The most useful comps are modestly successful films made at a budget someone would actually risk on a new writer.
Three is the right number: one for tone, one for audience, one for scale. Being able to say 'the tone of A, the audience of B, at the budget of C' shows that you understand your own script as a product without pretending it is a phenomenon.
Comps also correct the script. If you cannot find three, either the premise is genuinely unusual — say so, and comp on tone — or the script is not yet aimed at anyone, which is a rewrite note, not a marketing note.