Tough question. Matt is an exceptional guitar player, but there are those that can rival him.
Matt has a KILLER voice, with one of the most impressive ranges I've ever heard, and he is a far better singer than guitar player (and as I said, he is definitely no slouch on the guitar).
Then there are his lyrics, which are unparalleled. He is the absolute best writer of Christian lyrics in the industry. The lack of "Jesus is my girlfriend" songs definitely help.
. But he simply tells it like it is, and makes it poetic somehow too...crazy.
So I have to say he is the BEST songwriter I've ever heard, so that makes him best at songwriting, followed closely by his vocal abilities.
Although his sense of humor might beat it all....I love Rudolph VS Frosty, Skeletor goes to Mars, and the St. Anger parody.
edit: sorry for the bump....I noticed the dates AFTER I typed all that out...and I hate to see hard work go to waste