Each have had their PROs and CONs. For example..
I enjoyed Lower School (as we call it at my school) because being so young is just perfect. You walk around without a care on your mind, no one can blame that adorable smile on anything, best friends are as simple as saying "do you want to play in the sandbox with me?", teachers are paid to be sweet, getting high was seeing who could swing the highest on the swings, and finally, drama only involved plays and musicals.
I enjoyed Middle School because I was finally old enough to be aware of things and understand everything; however, I was still the perfect age where I couldn't get into any huge trouble. I disliked it because people were starting to figure out who they were, causing disagreements, drama, and other dilemmas. Plus all of the guys I knew over at our brother-school began experimenting with drinking and drugs. 7th grade was the hardest year for me, especially because I had a falling out with my friends and spent most of the year with only two or three friends.
I am still in Upper School, and currently I'm liking it a heck of a lot better than Middle School. All of the disagreements were in Middle School, so friends are already established, most of the guys I know have realized drugs are pointless, I'm old enough to have responsibility, and I can stop looking for who I am, because she's right here! I dislike it because with responsibility comes stricter punishments. Plus things out of school have been really taking a toll on me, including stress, worsening my academic and athletic life.
I'd have to say that my favorite grade was 9th grade, because I am currently in 9th grade, and things are still changing. I've always loved challenge and the smile I get on my face when I overcome something particularly difficult. The integrity of my friendships or relationships are sometimes challenges, but right now, I'm without a care in the world, and I'd love it to stay that way!
As for my favorite division of school (lower, middle, upper, etc..), I've had ups and downs in each of them. Everyday is better than the last.