Thanks to the quirky rules surrounding video game licensing, back in the early '80s it was often possible for two companies to release a game for the same system, as long as they did so using different media. With Frogger, this happened for two systems, the Atari 2600 and the Commodore 64. On the Commodore, Frogger was released on cartridge by Parker Brothers, and on disk by Sierra On-Line.
As for which Commodore version is better, it's kind of a wash. The Sierra version has somewhat better graphics and a more complete cast of characters. The Parker version has much better sound and no loading times. Both ports leave much room for improvement, but ultimately both are good enough, and owning one should not leave players wishing for the other.