A lot of editors will say they know if a book is MG or YA from the tone. How angsty is the main character? Super angsty and brooding? Sounds like YA. Tons of humor? Could be MG.
Subjective? Absolutely. As someone who writes humorous YA, I find the MG humor stereotype somewhat annoying. And I’m sure if you’re a MG writer who leans toward serious or angst in tone, you do too. Here are some of my favorite funny YA books if you’re looking for YA with comedy: An Abundance of Katherines, Spanking Shakespeare, and Memoirs of a Teenage Amnesiac.