Advertisements are the major limitation of almost all free website builder plans. The other big limitation with free website builders is domain names. Only Ucraft and Google Sites allow you to connect a custom domain name on plans (i.e.: yourdomain.com).
Otherwise you'll have to use a free subdomain. Some website builders like Weebly offer simple, readable free subdomains (yoursite.weebly.com)... While others like Wix are quite clunky (http://random1028.wixsite.com/yoursite).
The number one reason to use Ucraft's free plan is that it allows you to connect your own domain name (ex: domain.com).
Carrd is for building one-page websites. That's it. Because of that focus, it's also the best website builder for one page websites.
Webflow is really powerful but has a learning curve. It's not what I suggest if you're looking for an easy to use website builder but it is what I suggest if you want flexibility.
Many website builders limit features on free plans but Weebly actually includes lots of features: ecommerce, forms and unlimited pages. Even the Weebly app store is open to free users.
Google Sites is the only website builder that is completely free— they don't even offer paid plans. The thing is, Google Sites is not really a website builder for small businesses. It's more of a way to connect Google Services for a collaborative tool.
Jimdo has a very average free plan: SSL, 500 mb of storage, a 5 page limit and a decent subdomain (yourdomain.jimdosite.com).
XPRS doesn’t put advertisements on free websites— which is awesome. That alone makes it very worth considering.
Unfortunately the subdomain they provide free websites is pretty unusable and there is no way to edit it.
Strikingly's free plan doesn't include SSL. SSL is what secures your website— Google has said SSL is a ranking signal. When websites don't have SSL browsers will show a Not Secure message in the browser window. Not ideal.
The free subdomain that Wix provides is not as friendly as other website builders. Your free URL is: yourusername.wixsite.com/yoursite.
Finally Wix has a 500 MB bandwidth limit on free websites. You'll run into that limit quickly if you're getting much traffic— since the average Wix homepage is 1.4 MB. Other free website builders are more generous with bandwidth.
The major downside is that Wordpress.com randomly insert ads into your content. There's no way to control where the ads show— it's random. This is a big problem. With other free website builders you can at least anticipate and design around the ads.
HOW TO: ADD ECOMMERCE
Most website builders don't let free plans use ecommerce— other than Weebly and Strikingly which offer limited free ecommerce.
Ecwid lets you embed an online store onto any website. All you have to do is build the store on Ecwid and then you use their embed code to put it on your website.