Personally, I believe how 'hard' a subject is should be secondary to whether you enjoy it or not. Pick the subject that interests you most, or that you know you will enjoy the most. Then, look into the study design/past users' experiences if you want to get an idea of its difficulty level, if you wish. However, it's very hard to brand a subject as 'easy', as your easy might be someone else's hard. I know many people did tutoring for a 1/2 subject and then jumped straight into 3/4 (i.e. tutoring in year 10 for it, then the 3/4 in year 11). You could try something similar, or you could do tutoring in year 10 for a 1/2 then pick it up next year. I don't recommend tuition for 1/2 unless you are planning to only pick up 3/4, or unless you go to tuition while doing the subject. This is because it is very easy to forget all this information for next year, which makes your study useless.
Instead, learn one aos or even one unit of the subject you wish to do next year. Learn it really well. Then, by the time school comes around, you can use classes to consolidate your knowledge and focus on clarifying any doubts you have. While your class is focusing on the first area of study, you may as well be looking at the next unit, as you are ahead. This can be helpful, as long as you remember information and are able to understand and recall it. Don't fall into the trap of wasting class time because you are ahead, I did this at the start of the term for my 3/4 and I regret it now.
If you are able to pre-learn a subject, do it! But definitely not the whole subject, because you WILL end up forgetting almost all of it. Instead, familiarise yourself with the basics and focus on the first few aos' or even just the first one. You'll be fine!