- If a Pokemon has perfect Attack IVs, the stat will be 31 points higher than normal. The same goes for the other stats.
- Natures increase the stat by 10% not giving it any set amount of extra points; it variates throughout each Pokemon.
So basically, the answer variates between each Pokemon. Usually IVs will be more efficient in total, as 10% is rather low, and for Natures to be worth more, the Pokemon's base in the proposed stat will have to be very high. However, since IVs and Natures are two different attributes in one Pokemon, they can be combined together to have the stat relatively high depending on the base stat. Of course, EVs are very beneficial as well; usually these attributes combined is what you will find on a Pokemon with a competitive purpose.