Satch is so much more melodic and song-focused than Vai, who is more interested in provoking a reaction to whatever weirdness he has chosen to
call a "song". Satch's tone and phrasing are miles ahead, so much more pleasant to the ear. You almost get the sense that you could sing along with Satriani's tunes, which you almost never get with Vai. I will agree that Vai is a much better listen as a part of a band, rather than a solo artist.

I'll take Steve Morse.

Neither of the two listed, there are lot many other "shredders' who are legends and whose styles I personally prefer.

Both are great but Satch seems to have more depth in what he does, in any Vai piece he seems to come back to some similar threads in all of his pieces, maybe that is a signature for him but Satch comes off with more depth because of it

Satch has more feeling, he was a pioneer !

Becker

gee-tar has many many aspects.

I saw Greg Kihn Band with Satriani,

Joe has more command of structure and melody in song writing (IMHO)

Steve has more creativity in the solo dept (IMHO)

I saw Vai with Zappa, DLR, and solo. He does well as a side man/hired gun

I saw Joe solo and a Chickenfoot show.

My vote is neither cause I don't like any one more than the other

I couldn't really pick between the two. Great guitarists but I've never been able to quite get into either of them.

Actually I do very much enjoy the Alcatrazz album with Steve Vai, but on that same note I prefer Yngwie both in Alcatrazz and I like his solo stuff better than either of these guys' (Is it possible for me to talk about favorite guitarists and not bring Yngwie up? Probably not, sorry)

out of the 2 i prefer joe satriani simply because i find some of vai's stuff a little too avant garde, however i do love bad horsie by vai! there are many many instrumental guitarists who are just as awsome though joe stump, marty friedman to name just a couple.