As Marie mentioned,
"Green Cheek Conure questions" is a good place to start.
My GCC doesn't make any high-pitched noises. He has a "conure scream" that is rather loud but he doesn't do it very often.
He was very bitey when we first adopted him (he was 2) but now he rarely bites.
I wouldn't call him erratic. I can usually predict when he's going to bite based on his body language. I also know that he tends to bite when he's over-excited.
He
is nippy, but a nip is just that: a small pinch that doesn't break the skin. He is a strong-willed and opinionated animal to be sure, and he nips me sometimes to let me know he's unhappy, doesn't want to do what he's being told to do, etc.
That being said, I think my GCC is
very loving. He wants to spend most of his time cuddling my ear/neck/arm/hand or getting a head scratch. He does a hilariously adorable dance whenever he's excited, and he gets excited whenever he sees me or my husband in the morning, when we come home, etc. Even if I only leave the room for, say, 20 minutes, he'll do his little dance when he sees me enter the room again.
He reminds me of a puppy: he's adorable, he loves attention and human interaction, he's full of energy and loves to play, but he's also needy and demanding and will nip when he's over-excited. Also, just like a puppy, you have to keep a constant eye on him to make sure he's not getting into something he shouldn't be.
As far as training goes, I never tried to train mine until a week ago and on day 2 he could target a stick and on day 5 he could turn in a circle on the verbal command "circle" (with no hand cue). I'm working on "wave" now. He loves his little training sessions. Today when I would say "cirlce" he would do a circle and then wag his tail immediately afterward when he heard the clicker (but before he got a treat). He must have wagged his tail 15 or 20 times in the span of a few minutes.
Michael is right in that you need to research their personality traits and potential behavioral issues before you will know if it's the right bird for you. As an owner of a GCC, my opinion is different than Michael's (although I understand why he has the opinion that he has). Yes, I think that GCCs can make good, loving, trained pets.
BUT! Do your research first. The key word is
"can"...