I have used Pinegrow extensively (since 2017) and built a few sites with it. It gets the job done. It's probably the most open-ended website builder out there. It doesn't restrict you in any way, but it is not very easy for a beginner to grok, and it definitely requires a good familiarity with code to really be able to do a lot of stuff. If you can hand code, you'll probably have no trouble with it, but there is a bit of a learning curve to the interface. One big advantage of Pinegrow is that everything you do is live. What you see in the workspace is exactly what the site will look like. You can open multiple pages open at once, and multiple sizes of each page, so it can make building sites for different viewports pretty easy (especially since in now supports multiple monitors.) Pinegrow is the only one that will allow you to use third-party templates. You can buy a Bootstrap or Foundation or HTML5 template and open it directly. You can even open sites directly from URLs. In addition to various frameworks, Pinegrow has robust support for both flexbox and CSS grid. I would actually describe Pinegrow as more of a visual website editor as opposed to a builder. In terms of static sites, there's really nothing you cannot do with Pinegrow. And It produces clean, semantic code.
As for CMS, Pinegrow has it's own CMS-like features where you can make parts of pages "editable" by someone else who has Pinegrow, but it's not a true CMS. On the other hand, Pinegrow has a Wordpress version which allows you to build Wordpress sites, so that solves your CMS problem. There are discussions on the Pinegrow forums of alternate ways to build third-party CMS managers into a Pinegrow built website. You should probably look there for more info.
Of the three, Pinegrow probably gives you the most bang for your buck. They have an annual subscription plan, but you own the software. You download it and install it on your machine, and you can use it forever. If you want to upgrade it after a year, you need to renew. It's pretty fairly priced (I think it's like $175 for the year.) The developers are pretty good about fixing bugs and releasing new features. In the three years I've owned PG, it's had one major update (ver 4 to ver 5) and numerous smaller updates. The forums are fairly active, but newbies don't get a lot of love because most PG users are advanced and don't want to waste time explaining things like "what are media queries."
The program itself is rock-solid stable. I've encountered very few bugs, and the developers are very good about fixing them. They are also very good about updating the program often, and adding user-suggested features. This feels like a very tight-knit community. You'll generally get help in the forums pretty quickly, even if you're a total beginner.
What I like very much about BSS is it deployment model. You buy the program ONCE (which is VERY inexpensive) and get free upgrades for life (I would happily pay an annual fee for BSS.) It's installed on your machine, so you can use it regardless of your internet connection. BSS has it's own internal server, so you can preview sites in a browser LIVE as you work on them in the program, which is really great. The program auto-updates itself whenever a new release comes out, so you're always working with the latest version. There are no limitations on the number of sites you can build, and you export the sites as clean, semantic code with a straightforward folder structure. You could easily build a site in BSS, hand it off to a Bootstrap coder, and they'd have no trouble modifying it.
If all you need is Bootstrap (no CMS or database features), BSS is the best website building program you'll find. It's intuitive, stable, affordable, well supported and produces perfect code.
I cannot say anything about the actual builder beyond what I've read in reviews. Their own site is built in Webflow, and the code looks pretty good. They use a proprietary framework based on CSS grid (it's not a Bootstrap builder as I've seen it erroneously reported sometimes online.) I've heard there is a definite learning curve to their interface, but it's also supposed the be pretty polished and bug-free.
My biggest issue with Webflow has nothing to do with their software, but rather their deployment model. Webflow runs in the cloud, so you need an internet connection to use it. If your internet goes down (or something happens to their servers) you're out of luck. You can export the site's code, but without the Webflow software, I'd imagine it would be quite a chore to figure out how to make major changes. If you don't export your sites, they're locked into Webflow, so if you ever decide to quit their platform, you lose your websites. Also, their model is quite expensive. For someone with a freelance business, anything over 10 sites is going to cost you $35 a month. That's $420 a year, and you'll have to pay it EVERY YEAR to keep working on your clients sites. That's a total deal-breaker for me, and the main reason why I never gave Webflow more than a cursory looking over. I don't like being tied into proprietary systems (the same reason I never tried Adobe Muse, and look what a disaster that became.)
I tried it before Pinegrow and BSS, and I hated it. It's got a lot of limitations, and you have to pay extra for common sense features like code editing. The program is "free", but it's designed to nickle & dime you to death if you want to do anything substantial with it. It comes with a lot of templates but they're all variations on about 6 or 7 themes. There are a lot of pre-made blocks as well, but they're not not nearly as customizable as the ones in BSS. If you look at the Mobirise forums, you'll find over 80 pages of bug reports, and a huge number of posts from people who obviously have no idea what they're doing. It's the sort of community you'd expect from a free program that really caters to the drag-n-drop builder crowd. I'd stay FAR away from Mobirise.