As a character, Zell strikes a slightly unusual balance, and it can be a difficult line to walk in fanfiction. He's a loud, energetic teenager with a short fuse, a facial tattoo and a tendency to speak before he thinks. It's easy to assume he has other traits that often show up in this type of character. However, Zell isn't rebellious, reckless or ignorant.
Perhaps surprisingly, Zell is one of the more cautious members of the party and often serves as the voice of reason. During the field exam, he's the only member of the team to argue against leaving their post, and he tries to talk Squall out of taking the risky shortcut over the cliff. He's impulsive and sometimes fails to think things through, most notably when he reveals to President Deling that they're from Garden, but he regrets his mistakes, reflects on them and tries to be more responsible in future.
Zell is very enthusiastic about knowing things and sharing that knowledge, and it's pretty endearing. Hey, this train goes through an undersea tunnel; it's awesome! Do you want to hear about the history of Timber? He's not condescending about it at all; he just thinks facts are cool.
I'd consider Zell the most well-adjusted member of the main Final Fantasy VIII cast, probably on account of having been taken in and raised by a loving mother rather than a school for baby mercenaries. I love Balamb Garden as a setting, but there's no denying that it's messed these teenagers up.
'The most well-adjusted' is not a high bar. Even in Zell's case, he says, 'You tell us to go, we go. Even if it is a losing battle' to Rinoa when she's their client. The students of Garden have been brought up in the full expectation that, at any point, someone might tell them to die, and they'll just have to go ahead and die.
Given that Zell wasn't raised by the school itself, I wonder how he ended up at Balamb Garden. It's generally held online that Zell enrolled in Garden at the age of thirteen to emulate his grandfather. It's definitely mentioned in the game that Zell's grandfather played a role in the last war and that Zell looked up to him, so this would make sense, but I've had no luck hunting down the source for Zell joining Garden at thirteen for this reason. If you know where this information comes from, let me know!
I also wonder if part of the reason Zell enrolled in Garden was because his friends from the orphanage were there. There's definitely no canonical basis for that - it's entirely speculation - but it would make sense! It'd be a little sad if Zell joined Garden because he wanted to be close to his childhood friends, struggled to reconnect with them because they didn't remember him, and then forgot about their history together on account of GF use.
Zell may slip up sometimes, but he's a fiercely loyal friend, very energetic, very open in his admiration of people, with a strong sense of compassion and of what's right. He gets frustrated easily and he struggles to command respect, but don't underestimate him!