1. In a direct marketing campaign the advertiser is interested to target the audience who are most relevant to the business. The major metric to consider in this type is conversion rate, which explains about ROI. Most common campaign types are Search Network Only, Shopping Campaigns, Dynamic Search Ads etc.
2. In Branding campaign an advertiser needs exposure of his brand on major sites and applications. The most popular methods are Display Ads, Remarketing, Youtube Ads and custom ads target.