My experiences with each Nightfare so far:

>Wylder
Either total noobs or very skilled. The ones with the Artorias skin tend to be the worse ones.
>Guardian
Usually competent and pleasant, the kind of player that seems to enjoy the fantasy of keeping their team safe.
>Ironeye
The sweatlords of the game, complete tryhards. Most likely nightfarer to ragequit mid run by an order of magnitude.
>Duchess
They tend to not be very good but every once in a while you find one that understands she has better Int than Dex and they do really well.
>Raider
Almost always pretty good, always nice to see on your team.
>Revenant
I see her very rarely but the ones I see are almost always good, probably because only true Revenantheads play her. Seal hogger par excellence.
>Recluse
Can't opine since it's who I play.
>Executors
I picture Executor players as some frat dude baked off his mind playing in his dorm. They do not seem to really understand what they're doing.