From my perspective:
Joel
Pro - smart, multi-layered, unpredictable.
Con - sometimes over-serious, hard to read.
Nick
Pro - calm, easy-going, consistent.
Con - lackadaisical, half-hearted and indifferent about everything.
Harry
Pro - strong personality, upfront with how she feels.
Con - over-sensitive, moody, huffy.
Cristian
Pro - fairly innocent and naive.
Con - unsure of himself, forced, ill at ease.
Sam
Pro - fun and friendly.
Con - too desperate to fit in which makes her seem disingenuous.
Jack
Pro - honest, can't hide his true feelings.
Con - complainer, paranoid, grumpy.
Chloe
Pro - down-to-earth, caring.
Con - monotonous, far too desperate to appear normal therefore making herself boring.
Danny
Pro - dependable, defends his friends.
Con - flat personality, monotone, can't control his aggression.
The funny thing about this is that the pros and cons can sometimes be the same thing but just interpreted differently.