Frankly it depends on the mon in question and the exact IV spread. Since attack is the most important IV to me here's a couple examples of what I've done. I've utilized a high CP (L35) Machop with a middling average IV because it had a 15 attack IV. Meanwhile I've also turned my nose up to things with high CP/low attack IV for breakpoint reasons. I've also (and I hate doing it) trashed low CP/ high IV Pokemon if I knew I realistically wasn't going to commit the dust and candy to fully utilize them.
For raids, ultimately the one with the higher attack IV will do the most damage, so I focus on that. For defense you want higher HP and defense IVs, though ultimately they lack the same impact high attack IVs on offense have. I guess bottom line is the only IV that "matters" is the attack IV. The June 2018 Community Day article actually touches on it a little at the bottom of the Technicals: Catching and IV Checking section.
https://pokemongo.gamepress.gg/community-day-june-2018-guide
