Pick the channel where your ideal customer already spends attention and where you can get a real read on results within weeks, not months — for most early-stage B2B that's usually outbound, content/SEO, or a founder-led channel like LinkedIn; for DTC it's often paid social or influencer and UGC. Avoid picking a channel because a competitor uses it or because it's trendy; pick it because your specific ICP is reachable there and the sales cycle is short enough to learn fast.
Test one channel properly before adding a second — half-running three channels teaches you less than fully running one.