the idea behind this one is just asking what your favorite letter is in your music library. i.e. if you like Jane's Addiction, Joan Jett, etc. then your favorite letter is J.
for me, i'd have to go with S because of (alphebetical order) Say Anything, Schoolboy Q, Selena Gomez, The Shins, Silversun Pickups, Sky Ferreira, Skylar Spence, Sleater-Kinney, The Smashing Pumpkins, The Smiths, Snoop Dogg, Sonic Youth, St. Vincent, STRFKR, The Strokes, and Sunny Day Real Estate.
Mine would be "O" Because One Direction One Direction One Direction One Direction One Direction One Direction One Direction One Direction One Direction One Direction One Direction One Direction One Direction One Direction One Direction One Direction
Could you not have left that I in-between Goodbar and Stragger, Slowbro? Also... how about my favorite letter is H for Hard Out Here and Holding on to Nothing by Lily Allen and Hurting Me Now by Sia? (Or S or L... or B for "but why?")
edit: NVM MINDFUL POSTED. C. C is my favorite letter in my music library because my music library mostly contains songs my mom listens to that I don't know, and one of the songs in Solitude Standing is Calypso, which starts with a C.