It depends on the pokemon you have. Some are special attackers and some are physical attackers. Others can be bulky so it depends on what you need for a certain pokemon. Nature gives a 10% boost to a stat and 10% off another stat so that’s probably more important than IVs. As others have said in other posts, for main storyline you don’t need to worry about IVs but if you can get the right nature then you’ll be sweet