What is best APFS format for SSD?

APFS - preferred.

UNLESS, you want the files to be encrypted, then APFS (Encrypted).

DO NOT use Case-Sensitive unless you have a volume that needs to match Unix/Linux file system standards because you are going to bundle up the files and transfer them to a Unix/Linux system.

Otherwise as Kurt says, most macOS apps do not deal well with case-sensitive file systems, and it is best to avoid them, except when you have a special case situation where Unix/Linux are involved and the apps you are using depend on case-sensitive file names.

NOTE: I have been working as a Unix/Linux developer for 31 years. And all that time I've owned Macs. For the most part I have the most issues with Mac files that have "Spaces" in the file name, more than I've run into situations where the files I move between my Mac and Unix/Linux systems have depended on case-sensitive file names.

So keep your Mac apps happy, and do not use case-sensitive.

Just use simple "APFS".

It's all the same format. That differences are just wether its encrypted or not, or whether it's case sensitive to folders or not.

That is, if a folder name is differentiated because it has capital letters or not. So "foldername1" would be different to "FolderName1" for instance, when using case-sensitive.

Its entirely up to to you wether you want to have the volume encrypted, or not, and whether you want to differentiate between lower case and upper case folder names or not.

It should be mentioned that case sensitive formats throw off many third party apps. They either won't install, or won't run. Very few people actually need to use a case-sensitive setup.