The line depends on where and how you fish. If you are fishing open water #4 line will work. If you are fishing in structure you will need heavier line. I use #4 and #6 on my micro spinning reels. I use only #4 when I am in open water over tree piles or stumps. If I am fishing vegetation I will go to #6 to pull them out of the cover. If I am fishing heavy timber then I go to a heavier reel. Depending on the thickness of the cover I will go to a braided line, so I can pull decent size fish out of the cover. You just have to use your own judgement in different situations. Always use the lightest line you can get away with. Hope this helps.