Fishing line is a critical component to successful topwater fishing. Choose one that sinks (fluorocarbon), and you'll negatively impact the bait's performance. Monofilament and braided line are your 2 options - both float, and when tied correctly provide freedom of movement to the bait.
Bass pro Drew Benton relies on both for topwater fishing, opting for braid for some baits, but switching to a strong yet supple monofilament line for others. He outlines both in this short, straightforward video.