Lets see... as far as generally easy to work with, and what I would recommend in a rehome situation, would be the mealy if you did an amazon (they're one of the largest amazons and are far less moody and aggressive, but not as good a talker as the yellow heads), the blue crown or patagonian conure if you do a conure (again, larger conures so more mellow, not as piercing a scream as the jenday or suns, and blue crowns are the best talkers of the conures if that interests you), Alexandrine over ring neck (they're bigger (see a pattern?
dunno why, but the bigger the bird in a family, the more mellow they seem to be) and ring necks need a lot of constant handling to keep from being frightful and aggressive - a rehome ringneck might make a good pet, but will most likely NOT be hands on. ringnecks are generally not very hands on birds, even when hand-raised, unless they get constant handling), and if you do an ekkie I would lean towards male, unless you have the free time to handle a female.
Female ekkies, in the wild, are served by a harem of males. They literally live in a hole in a tree and only leave it 2 months out of a year, and the males clean the nest, feed her, preen her, and... well... mate with her
lucky girls, eh? The female can have anywhere from 1-5 males with her at a time. So, equate that instinct into a pet situation and you have a very demanding bossy bird. They still make great pets, but they take a little more time and attention than other birds. Ekkies are also very prone to plucking and having dietary issues (overgrown beaks are common, and they cant eat colored pellets or will develop foot shakes, spasms, clenchings, and seizures) and allergies, so again just a little higher maintenance. They are generally mellow birds, moderate talkers, and have a totally different "look and feel" than other species since their feather structure is so different, it's not oiled like a macaw or powder like a too, they're long thin, almost wiry, feathers with a different structure. Very cool birds
Whatever bird you get, it's still a coin toss on how they'll behave or react since you don't know their past, the owners can be lying about their past/age, etc. I'm sure you'll succeed with whatever you decide with some time, love, and patience
I know you mentioned in another thread you've worked with lots of birds, so I would just recommend visiting the bird in their home, if the owner is ok with it, and seeing if you two 'click' and how the bird behaves