Chiming in with another opinion that probably nobody needs to hear but anyway...
I'm firmly in the camp that believes a 4 person party feels too restrictive; certainly in terms of feeling forced to squeeze as balanced a party a possible into 4 characters and also because of the general RP flavour, party interactions, etc. It's by no means set in stone as we have the freedom to compose our party however we see fit but the standard composition of a balanced 4 person party might be: Melee specialist, Caster, Healer, Rogue. I find this creates a quandary of who do you take/who do you leave out? Bards, Rangers and Druids have some crossover with the aforementioned classes but are more hybrid.
For example, with 4 people max you are either forced to take a rogue or try to create another class which specialises in locks/traps and that just feels...strange? I can understand that certain classes (Ranger, Bard) might have have some ability in these particular skill sets but in general you would expect someone who has dedicated their life to a particular study/vocation would be an expert in what they have studied/practised. Generally speaking a Cleric, Mage, Fighter, etc. would not be expected to be an expert in lock picking and disarming traps...though of course you can roll a character to have these skills, at the expense of others you might require in game.
6 would be ideal but I would happily compromise on 5.
