This is something I’ve asked myself before - they’re both excellent singers with excellent range in pitch and expression, so I’ve always struggled to pick a favourite. The first album I listened to was Edge of Thorns, so Zak’s voice is imprinted in my mind in that regard, and his voice has a sort of clearer sound than Jon’s, but Jon seems to be able to put incredible energy into every note (like in 24 Hrs. Ago), you can tell he lives for the music. Even though Zak sings some of my favourite songs, and it wouldn’t be the same if someone else sang them, it pains me to say it, I think Jon is a better singer