As on 2023, from my experience I do not recommend BannerSnack at all. They are sunsetting BannerSnack in favor of a new tool that does not meet my needs.
I have yet to find a similar system that is as easy to use and comes with the type of support that Thrive Leads does. Sometimes support is a bit slow, but they always get back to you and nine times out of ten they can fix any problems on the first go. The flexibility of the form plugin itself is also excellent.
Thrive Leads can be easily used by anyone who has the basic skills to work within the WordPress environment and who has the knowledge about lead capture and segmentation. As a lead capture tool, I think it's use is restricted to obtaining contact information in different settings, which it does flawlessly.
In general, the support is great. When living in a different time zone, the support can seem slow but it's not. Most of the time, any issues I have get sorted out quickly and if it's not the first time, it generally gets fixed on the second go. Their knowledge base is good too although sometimes it's hard to search. Not usually their fault, more that users don't title their problems better.
In my opinion Canva > Bannersnack as of 2023. The features in BannerSnack are very similar to Canva, but long term they appear to be shutting down BannerSnack entirely.
I've used Optin Monster and Poptin on other projects. Both are good software for different use cases. Poptin is great if you are scrappy, just getting started, and you need a proof of concept and want to keep costs low until you've tested the market. Poptin isn't anywhere near as easy to use as Thrive Leads, but that $0 price tag is meaningful while you are just getting started. OptinMonster isn't as easy or intuitive to use as a builder, but the advantage is that more VAs have used Optin Monster as have used Thrive Leads, so you often don't have to do as much training. I would consider OptinMonster in cases where a website isn't build using Thrive Themes and where an incumbent VA is already well versed in the software.