Marmalead has been the go-to Etsy keyword tool since before most of its competitors existed, and the reason it still holds up is that it uses real Etsy search data rather than interpolating from Google. That distinction matters more than it sounds. A keyword that looks strong in a generic SEO tool might have almost no traffic on Etsy, where the buyer intent and vocabulary are different. Marmalead's engagement score rolls search volume, competition level, and historical trend data into a single number that tells you whether a tag is actually worth using.
The $19/month price point is hard to argue with if you're running more than two or three active listings. A single listing that finds its way into a better keyword bucket can pay for months of the subscription. The main competition to be aware of is eRank, which offers a meaningful free tier and a slightly more modern interface. Marmalead wins on the depth of its trend data and the Storm brainstorming tool; eRank wins on accessibility and price for sellers just starting out.