While certain subjects may be easier to do an extended essay in, your performance in it solely depends on how interested you are in the subject and how much you are willing to work for it. Keep in mind that the extended essay is a year long research paper, consisting of 4000 words in total. Hence, picking a subject of interest is crucial as you may face various challenges along the way and must remain constantly motivated to overcome them. 

Generally, doing an extended essay in literature compared to computer science or physics would be relatively easier and a lot more flexible. Especially if you are an avid reader, it should be a walk in the park for you. Students most commonly comment upon a theme or a certain literary tool from a book or compare them with other books. It gives you ample time to re-read the books and research them. 

On the other hand, finding a research question itself could be quite challenging when doing an extended essay in science. Whereas forming the methodology and conducting the experiment requires a lot of research, patience, effort and time. Your research must also be original, unlike the IA. Statistically, physics and computer science extended essays have gotten a lesser percentage of A’s. If you are genuinely passionate about it, have plenty of original and creative ideas and willing to dedicate a lot of time to your extended essay, only then must you take it up.