I've had quakers for about 15 years and bred them. They are the cutest, most adorable little babies. Baby quakers give the most gentle kisses. Then they grow up and its hit and miss. Mostly miss. My major gripe with quakers is they they scream a lot and they like to shoot their poop through the cage bars so it slides down the wall. Most of my quakers have done this. They are super smart, but hormones are no joke at maturity. They can go on and on for years with territorial screaming every time you come into the room, attempting to bite through the cage bars, running at you to bite if they are out playing on top of their cage, screaming every time you move something in their territory(the whole room where they live not just their cage), or bring something into their room. Basically, if something moves, they are screaming about it. I can see why people like them, but I can also see why equal numbers of people dislike them. Personally, they are the one species I always kind of regretted getting into. If I want to take a nap in the afternoon, I can get two cockatoos, a hyacinth macaw and 5 yellow napes to be quiet, but the quaker will start up and go on and on for 20 minutes or so, quiet down just long enough for me to sleep and think he's done and then he'll be screaming again. I have two bachelor male quakers right now and they are the ones that get everyone wound up first thing in the morning to start screaming, the ones that start random screaming fests throughout the day and the last ones to shut up at sunset. My older male is the one that screams the entire time I'm in the breeder room cleaning cages. Doesn't have to be his cage, I moved something in what he thinks is his territory and so he's screaming the whole time. Lets not forget having to put up a shower curtain on the wall behind their cage due to the poop shooting.
Personally, I'd gladly rehome another cockatoo than a quaker. Quakers have many fine attributes, they just are not my favorite. I would put their intelligence up there possibly around that of a cockatoo with similar neurotic tendencies plus aggression and screaming X 2. And poop shooting which I've thus far not known a cockatoo to do often enough to bother me. Thankfully, my experience anyway has been that their bite is painful but not much to get overly excited about. It might bleed and bruise a bit, but considering the level of aggression, the actual damage done is typically fairly minimal. You still bleed and everything, its just not that bad compared to some similar sized birds.