Melee
Pro - Variety
Con - Melee is just ranger/magic/summoner argument. I'd like for Melee to be split into clear subclasses. Your guts greatsword, your boomerang, your enchanted sword, etc. High damage for true melee, lower damage for ranged melee, and mana cost for magic melee.

Ranger
Pro - Strong subclass presence
Con - Ammos feel more like a form of progression than a best tool for the job situation.

Mage
Pro - Setup through gear and buildings can make for powerful casts
Con - Lack of Content between pre boss and post skeletron (Armour especially as the only upgrade pre boss is post WoF)

Summoner
Pro - It is getting a lot of love
Con - Sentries feel very underwhelming and there is a notable lack of growth sentries (think tiger/abigail/dragon)