Flutter seems to have a lot more people using it atm @pillaiindu - and this usually equates to more books, videos, resources etc. For instance there’s @carminezacc’s #book-programming-flutter but I don’t know of any NativeScript books.
However as mentioned in response to @DevotionGeo’s post I would delve a little deeper into both and see which one you prefer yourself… but if I were choosing right now I would be leaning more towards Flutter because I really like learning from books 