The South is very OK. But be advised that you can end up in serious winterweather in the Atlas, High Atlas, Anti Atlas and Rif mountains.
I was there in May of last year and I have never had such a nightmare riding conditions. We pretty much worked our way out via tar roads but even that was hard work.
I wouldn't go into the high mountains. Although I think the South side of the Anti Atlas will be ok.
Take your time to explore the south to it fullest! Some beautifull stuff to discover.
Wish I could head out there again this winter... boehoe.
If you want a little idea about the winterconditions check out the pictures on my website below.