When you get down to it, this competition isn't about who can sing the best. We obviously learn this from season 1, because Suzie was by far the best singer. The competition is to find who's best for Supernova. In my opinion Magni would fit best.
The reasons the other three wouldn't fit the band are these:
Lucas - has too many voice issues. He is constantly off key and too screechy. Yeah that works with some songs, but it just not enough to pull it off on all the songs. He has a unique voice and I think he would work better with his own band.
Dilana - where do I start? She has a pretty good voice and it's certainly different. Then again I don't think her voice appeals to a wide variety of people. I think she overpowers the band sometimes. Dilana would certainly work out better as a solo artist.
Toby - he's my runner up. He has a solid voice. He can jump between melody and wailing with ease. But he can , at times, have problems being out of tune or off key. Again I think he would work out better as a solo artist or with his own band.
Now Magni.... you can't deny that his voice is the best out of the four. He is constant, and he can sing melody and he can wail. One of his key attributes is that he doesn't overshadow the band. I mean come on, you've got 3 music icons. Do you think they really want a newbie coming in and stealing all the light. Plus these guys are to go on tour in just a few months. They don't need a singer with voice issues. They need someone who can jump in and get it done and Magni is it.