I'll think about it first, rather jumping into conclusion because DS is "original"
Capacity: DSi, tons of memory and such; DS not so much
Games: DSi, Large App-Like system; DS able to play gameboy AND DS(i) games
Durability: Well, I've dropped my DS on concrete several times on accident and it still works pretty well; DSi would probably break the first 2 times you drop it
Cost: DSi cost a crapload of money; DS is cheaper
Conclusion: DS: 3 DSi: 2