Thunder Bugs, the lures, not the bug, are available in size #00 through #2 making them perfect for both panfish and all sizes of stream trout. The size #2 Thunder Bug is also great for smallmouth bass and walleye.
Whether you choose to use plain or dressed Thunder Bugs is strictly a personal preference. Lure size, however, is important. The rule of thumb is use smaller lures to catch smaller fish and larger lures to catch larger fish.