In my opinion, the best written evidence from my Batxillerat posts is one I wrote some days ago: Are you a popu?
I think this is the post that depicts my writing skills best. I was very inspired when I wrote it, just after watching some videos that made me think deeply about the situation of many teenagers in Spain. So I guess I just let all my expressivity go into it. I consider it to be my best work because I think it's where I managed to use the language in a better way, making it sound very natural. I used some colloquial words but I believe this contributes to make it sound more energetic. I like the structure and phrasing I used to express my opinions, especially the chain of rhethoric questions in the end. Regarding vocabulary, I think it's varied, non repetitive and natural sounding.
While I was writing my posts I didn't think about which one was the best. I'm not completely sure this is the one, as I have other posts I also like, but I think it's a good example.