I'd pick accuracy. Cheap impressions look good on spreadsheets but mean little if they reach people who won't engage. High-quality targeting reduces wasted spend, boosts relevance, and lifts conversion rates, even at higher CPMs. Good targeting also gives clearer signals for optimization: which audiences respond, which creatives work, and where to scale. That said, CPM matters when scaling a winning combination; if targeting is nailed, lower CPMs improve ROI. So start with targeting quality to find what converts, then chase efficient CPMs to grow that success without sacrificing relevance.