Our last newsletter/blog post was all about the different VCE Englishes! 🙂
Overall, I would say that mainstream English (the new study design, anyway) is really about learning to master different kinds of writing and analysis for a variety purposes, audiences and contexts, while English Language is learning about English as a language system.
In English Language, students systematically examine the English Language as a language system, so it's really a study of linguistics. There's a lot of metalanguage you have to learn (which can be a pro or con, depending on your brain), and students are required to explain what is going on in terms of language features, processes and purposes in a given text. You still have to write essays, one of which is quite different to anything you may have written before, called an analytical commentary. It is less subjective than English or Literature because there are right and wrong answers, but there is still a high degree of analysis that's required.
In the current study design for mainstream English, the focus is on the student’s ability to analyse very wide range of texts as well as writing for clarity, accuracy, expression and sophistication. So there are quite a few texts you'll have to master, analyse and demonstrate fantastic knowledge on. Some students really enjoy this variety and others really struggle with the breadth required.
Unfortunately I don't know very much about other subjects, but I hope this helps you decide on your English one!