Decide who maintains the site, not who builds it
Choose for the person who will update the site after launch. Squarespace allows 2 contributors on Basic and unlimited from Core, and its Website editor role can change content but not add pages or styles. Wix allows 2 collaborators on Light, 5 on Core and 10 on Business, while WordPress.com allows unlimited users on every plan. Webflow sells content-editing seats at $15 a month billed yearly, and Duda limits each client account to chosen sites and permissions.
Check the exit before you commit
WordPress.com exports posts, pages and comments as a standard WordPress XML file, without the theme design or plugins, and Squarespace exports pages and one blog in the same format, leaving store pages and custom CSS behind. Webflow's code export, on a paid Workspace plan, and Duda's Site Export, from its Agency plan, give static files without the store, CMS-driven pages or working forms. Wix sites can't be hosted elsewhere, and Wix says blog posts can't be exported.
The plan price isn't the whole bill
WordPress.com is the builder here whose yearly prices are first-term prices: Premium's $8 a month renews at $9, and Business's $25 at $28. Selling adds costs too. Squarespace Basic takes 2% of store sales, Webflow's Ecommerce Standard 2% of each order and WordPress.com's payment blocks up to 10%, all on top of card processing. Duda sells each site's store as a separate subscription from $8 a month, and Webflow bills team seats apart from site plans.
SEO capability differs more than the marketing suggests
All five set page titles and meta descriptions, WordPress.com from its Premium plan. Webflow and Wix document the most beyond that: canonical tags, structured data, 301 redirects and control over robots.txt. Duda takes wildcard redirects and schema markup and lets you replace its sitemap and robots.txt. Squarespace handles redirects but generates its sitemap, robots.txt and structured data with no way to edit them, and WordPress.com leaves manual redirects and schema to plugins.