As I understand it, the Strand Based hairs are a recent thing, introduced with G9, if I remember correctly.
They probably play better with dforce, if that is your thing. It isn't mine.
Just recently, they have started calling the earlier legacy hair styles Card Based to distinguish them.
I could be wrong, but I'm sure someone will come along with more in depth knowledge than I have to explain in more detail.
Strand based for still images; card based for animations.
Render animations/frames is super slow with strands in Blender, Reallusion or UE5, even with pretty good GPU.
Good thing is that strands can be converted to cards via Hair Tool for Blender
Ok so that's a little more confusing to me. I use Genesis 8 and preferably G8.1; no animations for me. So should I look for card or strand based hairs?
You can use both, I do.
Strand based looks better in closeups because of Dforce sim, but it's pain to set it up right.
If you are not animating, there shouldn't be any problem for you. It's all about render time per frame.