Petrucci is easily as versatile as Vai...they both come from a similar background, and have a lot in common. Having said that, since his name was brought up, neither one of them can touch Guthrie Govan. All those years Guthrie spent teaching and transcribing turned him into a total freak of nature. He's essentially the pinnacle of versatility in electric guitar playing. Blues, jazz, rock, shred, country, bluegrass, fusion, slap guitar?! Fretless?! It's like, alright dude, we get it - you're untouchable lol. He definitely wins up against most in the versatility department.
That being said, I prefer Petrucci and Vai's music over Guthrie's, seven days out of the week. To my ears, they are way more lyrical, and their compositions are way more interesting to listen to.