IT is how to use a computer whereas CS is how to program and how the computer works
CS is alot better because if you can do CS you can do IT
IT no longer exists at GCSE. There may be an alternative though such as iMedia.
Computer Science is now 100% exam. You'll have more options with CS and it's recognised as a backup science for the EBacc. Definitely a helpful subject if you don't take it any further.
I've met very few students who don't regret taking IT unless it's something they're super interested in.