whoa thats a really tough one and rinnekugan has a good point except kakuzu has a varietty of long range attacks as weve seen so he could be attacking deidara even while deidara's in the air and lets not forget deidara can't afford to wastes any explosions because he's always limited on his clay
kakuzu can use five all elements, he can use combos, such as fire+wind, also he has 5 life, he can hide one heart and fight with deidara with four, after all he can restore with one hidden heart
I'm going with Kakuzu because of lightning release and being smarter. I feel on any lucky day Deidara can kill almost anyone because he can fly up high and drop bombs right after another