I also have a Green Cheek Conure and she is just like Marie's. The switching loyalty thing is so true and you can't give them enough attention. In fact, they are Velcro birds. It's not enough to be near you, they want to be on you. Which means they need a lot of out of cage time with your attention. Thankfully, I have long hair so Emmi just hangs on to my pony tail while I do what I need to do around the house. Lol
They are little hams. They will do anything for attention and know exactly how to melt your heart to get what they want. From rolling over to hanging up-side-down to dancing...Emmi dances a lot and sings her name to a beat. She will do this for attention or just because she hears a song that moves her.
Emmi is a pretty good talker and has said well over 20 phrases, but she seems to forget some and move on to others. So I would say she says more like 10-12 things. She seems to use short cuts too. "Are you ready?" Has turned into "Ready?" Also, their voices are very small, quiet, and robotic. I'm positive she can say more, I just can't understand her. They do speak in context. If she needs to go and we are not near a perch, she looks around and says, "Go potty! Go potty!" Before taking off to find a perch.
Emmi is very eager to learn tricks. She gets so excited when she masters one. All I need to do is touch her treat jar and I can see all her tricks without asking. Lol
They are FAST! Emmi can run really really fast. She can fly even faster. She is very very good at getting to something she should not have, before I can even comprehend she's there. Lol
Watch out when they get mad. They bite to kill. Lol It can draw blood, but they are very small compared to a bigger bird. They can be trained out of it and we have trained her somewhat. They give good signs they are about to bite though. Emmi gets low and fans her tail a little to a lot. I've static shocked her a few times by accident and she's gone into attack mode and won't give up. She has chased me around the room for this! I don't blame her! Lol
Emmi is pretty quiet, but we do give her a lot of attention so no need for contact calling. In fact. She's learned to use a bell to call to us (we taught her that by coming to her when she rings it. I've heard that they can get loud, but it's still not as loud as a Sun Conure.
But if you are looking for a bird that loves to cuddle, is friendly with everyone in the house, and who can be a constant buddy...a GGC is the way to go. They really are a big bird personality in a small package. But I agree with Marie. Emmi would attack Parakeets if annoyed too much. They can be bullies with small birds I've heard. I totally believe it.
Edited to say: Please see my responce on your other post, "My next bird!" I was not aware you were having trouble with your parakeets and I do hope you give them a chance before you get another bird. I'm sure you will very happy with them if you try a little harder to gain their trust. Good luck!

My family: "Emmi" Green Cheek Conure (12/15/2012), One husband, two step kids, and one baby boy born in January 2015!