The verdict
If your process is built around agreements, intake packs and approvals that need signing and filing, I'd pick airSlate, and I'd ask for a demo of altaFlow specifically. If you need branded forms, applications or surveys that write cleanly into HubSpot, Airtable or a payment tool, I'd pick Fillout.
Many small teams will find Fillout easier to start with, because it has a free plan with a real response allowance and you can see what you are buying. airSlate sells by quote, so treat the quote as the real number. Do not buy airSlate for the odd signature. A lean e-signature tool is quicker. Do not buy Fillout for one simple contact form either. Simpler tools do that for less thought.