Worms such as nightcrawlers and red worms are awesome baits for sunfish. A small piece of worm is all you need. Just make sure you rig it on a small enough hook so the sunfish can get the hook into their mouth.
Nightcrawlers are larger worms, so most of the time, you are going to be using smaller pieces of these worms when targeting sunfish.
Red worms are much smaller worms and they are the perfect size for sunfish. Most anglers will use the entire red worms when fishing for sunfish.