Bazzite is definitely a great option if you have an Nvidia card or you are looking for gaming performance. It includes some gaming oriented features and optimizations like the System76 scheduler that aren't in the regular Fedora Atomic builds that have the potential to increase performance, and make things easier (such as having a build with Nvidia drivers in the root image). I don't really game at the moment, so I don't have personal experience with Bazzite, but I've been on Fedora Atomic KDE for a while now and it has been a great experience. I've heard lots of great things about Bazzite, so I would expect it to be a similar experience (maybe a bit easier). I feel comfortable recommending both, but the more appropriate choice will depend on what you use your computer for and your own preferences, of course.

While I haven't personally rebased to a different image before, it should be pretty seamless, except for some potential config issues if you are switching to an image with a different DE (i.e. switching from GNOME to KDE). I've seen people in this community mention successfully rebasing to another DE, but Bazzite's documentation recommends against it. I imagine that there may be config issues in /etc or in your home folder from switching DEs, just as may be expected when switching to a different DE on a non-atomic system. Your milage may vary there, essentially; Fedora and uBlue just don't officially test rebasing between different DEs. I usually tend to be cautious in my recommendations, so I generally recommend users to try out different DEs on a VM before deciding on one, and to do a full reinstall when switching DEs. There's a chance that is overkill, but it is certainly safe. Here is a blog post detailing some issues a user had when rebasing from Silverblue to Kinoite as an example. It seems that the issues can be fixed, but since the rebase between DEs is not officially tested, it is prone to small issues like these (though it appears at least some of the ones in that post have been fixed upstream now). The issues in that post were all incredibly minor, so you could likely fix your system in place if you were to try this (maybe you won't even have any issues; half of the post was about an issue caused by the fish shell, which is not the default), though you'd have to know where to look to find any issues (I'd start by checking overlaid packages and seeing if there are any from the old DE). You can always rollback safely, as each previous version the OS saves has it's own unique /etc folder (even though it isn't part of the root image).

Switching between Fedora Atomic and Bazzite is more supported (when you keep the same DE), but different images can add and remove packages from the root image, so you may find that you'll need to overlay packages/remove overlays when switching between them (such as Nvidia drivers). I don't imagine that posing an issue as an end user in most cases (outside of the Nvidia drivers), just thought it was worth mentioning, as it is an edge case that could pop up. That's one of the reasons that adding overlays isn't the first recommendation for installing packages, as they have the potential to make rebasing a bit more complicated for a handful of packages that may be different between different images. I would imagine that an update (or even the rebase itself) would fix any dependency issues (hence why I don't see it being an issue for an end user in most cases), but I don't know that for a fact. None of my information on rebasing is based on experience, except for rebasing to a new major version (i.e. Fedora 39 to Fedora 40), so you should look into that more yourself if you want more concrete details. Also, I mistakenly mentioned rebasing to a previous version of your image from before an update. That is actually called a rollback, and uses the rpm-ostree rollback command, more info here (I've edited my previous comment to reflect that). Bazzite has some good documentation on rebasing here, and I don't see any mention of package conflicts between Bazzite and Fedora Atomic, though you will likely want to remove an Nvidia driver overlay if switching from Fedora Atomic to Bazzite. You very likely won't need to make any other changes. There are people in this community with far more rebasing knowledge than I can provide/find from searching, so you can always make a post asking about it if necessary, and someone should be able to help.

It's also helpful to note that documentation for Fedora Atomic (sometimes you get better search results by using "Silverblue", as that was the original project name), Bazzite, and Bluefin are often interchangeable, as they are all based on Fedora Atomic. You may find some things more easily documented in Bazzite/Bluefin than on Fedora Atomic or vice versa, but much of that documentation applies exactly the same to any version. For any additional information about rpm-ostree, I would unironically suggest reading the manual page through man rpm-ostree or online at a site like this if you aren't comfortable with the terminal interface for man pages (quick tip: you can search for a term in man by typing / followed by the search term, and you can use n and N to go to the next/previous occurance).

I'm just here to help people out when I can, so if my comments are able to help anyone, I see it as time well spent. Sometimes it even helps me learn new things myself, and cements concepts I was already familiar with, so it's mutually beneficial!