There is no universally best channel. There is only the channel that matches your demand type, your sales cycle, your margin and your ability to produce the assets it needs.
Start with demand type. If people are actively searching for what you sell, capture that intent first — it is the cheapest path from stranger to customer. If they are not searching, you have a demand creation problem and paid social or content becomes the entry point.
Then set a stopping rule before you spend. Decide in advance what evidence would prove the channel viable and by when. Channels rarely fail loudly; they drift, absorb budget, and get defended out of sunk cost.