I would say GCC's are the most forgiving of these birds if you are new to birds. Senegals, while still great birds, can be a little more sensitive or nervous, less so if they are properly fledged and socialized of course. And they are more likely to be aggressive to new birds, if you think you might get more later on. Caiques can be so high energy that they have their own challenges. Caiques also generally need larger cages than other birds their size, because they are so energetic and prone to getting into trouble.
All of course can be cuddly, playful, social, and will enjoy all the attention they can get.
My GCC is not a perfect bird - she can bite if someone she doesn't like tries to pet her or pick her up sometimes - but her bite strength is much less than a Senegal or caique's. She is gentle with other birds, not a troublemaker, she loves to snuggle and cuddle, is very trainable and responsive, she is very quiet except when someone is vacuuming or washing dishes - she is basically just a wonderful loyal little companion. Basically you get the cuddliness and personal hygiene of a cat with the trainability of a dog; the downside of course being that she can bite some people, and likes to also chew on fingers (this is done very lovingly, in an attempt to preen, but is still rather annoying), and can make a big mess. She is very good about not pooping on people, and will fly to her perch to poop if it's convenient for her; however she has no qualms about pooping on the floor, or throwing food around.
You need to see what the grown ups are like. 
