Honestly? I've stayed in "every" Marriott in the greater San Diego Metro area and especially compared to NYC, the entire area is "relaxed"; even the Convention Center Plaza area isn't very loud or crowded (except maybe on game days, which means avoid the Gaslamp Courtyard I guess).
And I was in the Coronado Marriott over Memorial Day weekend; the weather was gray and chilly so it wasn't very crowded but even still it probably meets your needs.