I guess when it comes to groundcover, there are many choices. What kind of groundcover do you want. Is it for walking over or basically to look at.
I think ferns for groundcover will, with time, become kind of unruly and jungly, and not necessarily be appropriate to walk through them. Then again, there may be no maintenance required, like cutting the grass, and the biodiversity will benefit micro-organisms, worms, insects, etc. Ultimately, this groundcover environment benefits any fruit trees you may have planted. I see where you're going with this. You'll also ultimately save money on fertilizers because of all the biodiverity (microrisy).
Personally, the ground cover I like, is the one that grows closest to the ground and is really good at preventing other weeds from growing. And, requires very little, if any, maintenance.
To be honest, I'm not sure if my favorite ground cover, described above, even exists, I just hope it does and that I will someday find it.
Maybe having a combination of both is best. A groundcover area of ferns and a different type of groundcover in another area (say a walk path).