how do you lot choose a marketing channel?

Start from where your buyers already go when they have the problem. If people search for the thing, search ads and SEO. If they don't know it exists yet, social or paid social. Big-ticket B2B, LinkedIn and plain outreach. Then pick one, give it a fixed budget and two or three months, and judge it on cost per lead or sale, not likes. Every small team I've seen struggle was running five channels at once and never found out which one was working.