Yeah.. all the while is more personal preference...

Both of them are great players but to me, Vai controls his instrument and makes his instrument speaks, cry, scream, angry, laugh... Which is why I admire... I always think his song always has a story in it.

While Satch's improvising is somehow great. Some simple song such as Ten Words are just very beautiful. It is not hard but the feel and the whole thing Satch composed is just simply beautiful.

For singing? Music is an art.. so there is no rule in which kind of singing is nice. Even shout and yell like Dani Filth (Cradle of Filth) is still part of singing. It just depends on your style. Of course, when you singing something angry, of course you cry, scream, shout and sometimes ur vocal is not so clear to be listened but tell me in this world, does someone sing happily and clearly when he sad and angry? Of course he shows his emotion, scream.. and when he sings in a sad mood.. some words come out are blur. When ur gf cries, something the way she talks is not clear too right?
Hehe this is music, that's why for me.. I nvr focus on what the fella sings on the music. I try to understand. Sometimes I read the lyric and to get the whole meaning of the song. So when I listen to it, I just feel it.. not concentrating on what the fella talks but feel all the elements in the music. such as the drum beat, guitars, piano, violin etc.

Of course, this is my way of listening.