Anything from piggie parcels is good!
However, it’s going to come down to what your piggies like. Personally for a first purchase I would go with single bags so you can see what your piggies prefer.
I really like the look of the letterbox forage trays, however, none of my six animals like any of the the flowers so it would be a waste for mine. Mine love all the dried leaves - plantain , hazel, strawberry and raspberry, nettle, birch and dandelion. They also love the green oat and cucumber slices. i also buy the dried carrot but due to the sugars that is given only occasionally as a treat.