"its going to be hard to top this" means that it is going to be difficult to improve or make better. For instance, "the movie scene was so good, its going to be hard to top this" would mean that it would be difficult to make a better scene.

It means that it's so good that it will be hard to find something better.

It means that it will be difficult to find something better

Hello Abigail, Yes I agree with Justin and Eric, this expression means that something is so good it will be difficult to find something better. I hope that helps, Christine