Best Art: Terminate
I can't actually put my finger on why I like this art, but I know I do. It's just an amazing piece of art that really fits the card well. I much prefer this to the modern art (apologies to Wayne Reynolds).
Worst Art: Cloud Spirit
Giant cloud monkey? I don't know; I just think that this is an instance of DiTerlizzi's art tipping too much into the "kid-friendly" pool. To be fair though, the other art for this card isn't much better,
Most Ill-Fitting: Elephant Resurgence
Now, there's only one reason this is the most "ill-fitting" art: it's a sorcery. This art screams "instant"! Admit it, if you just look at the art, you hear a "sproing" as the elephant leaps out of the ground. I know that this isn't DiTerlizzi's fault since artists probably aren't given the full specs of the card (or necessarily knows how to play the game), so I blame WotC for this! Curse you WotC for not giving us more instant-speed elephants!
Check out DiTerlizzi's body of work here. You will not be disappointed!