For CS depends on the exam board really. OCR is a whole other mess. The exam board people don't know what they are doing or what the content is. The amount of incorrect mark schemes is ridiculous. They also put A2 content into the AS exams, so clearly they don't know the syllabus. The amount of content to learn is crazy, then most of it doesn't even come up,don't know how they expect teachers to teach all of that + doing the coursework. Almost all textbooks and mark schemes contradict each other and this one time, my teacher asked OCR a question (My teacher is part of an OCR facebook groupchat where you can ask question and the OCR Computer science people can answer) and different OCR ppl were arguing over which answer is correct, cos clearly the don't f*cking jack about CS.
(LMAO as my teacher said, all CS teachers are sh*t at CS cos, if you had a CS degree, why on earth would you go into teaching? Being a developer would pay A LOT MORE)
OCR may be the easiest exam board in terms of content, but new syllabus is messed up, no one knows what they are doing. Unless you are doing CS, Physics, Maths, Engineering etc at uni, CS may be my favorite subject but I would suggest doing Biology. Only put up with CS if you are really passionate about it. (Liking the subject even before GCSEs)