Why would you seek to discuss who is better among beings you don't even believe in?
Humoring the concept going from biblical text, as there are alternative views, you have on one side a being who is believed to have created everything in existence, is all knowing, etc... On the other side you have the rebellious son who was essentially eternally grounded for disobedience and who is believed to have filled the world with much sorrow, is referred to as the father of lies, etc...
Now, going by biblical descriptions and accounts I would say God is better, but there are many various views by not only those who believe in them but those who do not. In the end its a matter of opinion though your bold statement that they are both fictional is not a belief shared by everyone.
If all that the bible says is true, then I would say there is a need for both. Without the temptation of sin, there would be no perseverance and virtue of humans through the struggles of life. If we only had the rules of biblical Satan, superioritywouldn't exist since the only philosophy would be our wants and desires, therefore no improvement on our species could be made. With only God, there would be no race for superiority, since there would only be Eden; no temptation, and no struggle. The presence of both create a tug and pull for those who choose the path of goodness, or those who choose degeneracy.
This all being said in context if of biblical truth. Not my truth.