Hello!
This is a very subjective question and it really depends on who you're asking, and their tendencies to be objective/subjective in giving their thoughts and opinions.
For me personally I found it WAAAY easier to write 评估文 (evaluative piece) as compared to 劝说/说服文 (persuasive piece) for a few reasons:
1) I'm not too opinionated when it comes to things that aren't political, which won't come up in VCE Chinese anyways, so writing a piece that evaluates the positive and negative aspects of things is much easier.
2) I find that I can write more when I talk about the different aspects of things. (some people don't like it tho)
3) Might sound lazy but you can almost always end my piece with 综上所述,利弊共存,正所谓:“河有两岸,事有两面” or something like that in 评估文 and the essay quality will just go downhill from there but you have to come up with something new for every persuasive piece which might not be ideal at times.
4) Trying to make your language sound persuasive can be a challenge if you are emotionless. (that's me)
Again it's just my opinion so yeah.
From what I've observed myself tho, and what most teachers have said, people tend to write 劝说/说服文 more regardless of the language, but it always depends on the year because sometimes the persuasive essay is harder.