I can honestly recommend both pionus and poicephalus. However, they are VERY different from one another.
First difference - noises. Pionus are louder, but poicephalus (senegals and meyers) voices are more shrill. I would really recommend that you listen to both types of birds before you make a decision. The pionus noises don't bother me at all, but they do greet the dawn every day, and it is loud. Pionus can also develop into problem screamers, and if you would get one of those, they are a problem, although very few actually become problem screamers. The only people I know personally who have pionus who are problem screamers have white caps. They can make a noise that sounds like a fire alarm, and they can make it incessantly. This is rare, but it does develop in some pis. My pi is not a problem screamer at all, but she will scream if she is left alone, and she won't stop until she has company. You wouldn't have to worry about that in your situation, if that is all that happens, because you have Maxx. Bird company is as satisfactory to most pis as is human company.
Poicephalus make a call that to some people sounds like nails on chalkboard. IF it sounds that way to you, it will be unbearable. My younger son is really bothered by my senegal's call. I also once met a woman who rehomed her meyers because she had the same problem with the scream that my son has. I am not bothered one bit by the poicephalus call, neither are my older son or my daughter. My mother, who also lives with me, can't even hear Roni because she no longer hears all tones, and that pitch happens to be something she can't hear.
Second difference - personality
Pionus are MUCH clamer than poicephalus. Both birds can become frightened. When pionus become frightened they wheeze and generally sit still. When pois become frightened they may fling themselves around or bite as a defense mechanism if they can't get away. (Senegals as a species are known to be more easily frightened than are meyers as a species, but you could get a more nervous or less nervous individual of either species.) Pionus are not nearly as easily frightened as poicephalus.
Poicephalus are not as active as green cheeks, but they are much more active than poinus. Poicephalus love to cuddle and participate in training. They are really fairly similar to green cheeks, but they are slightly less "wired". They do eat a bit more than green cheeks and go through toys a bit faster, but not much moreso. My senegal bites much harder than my green cheek, but she doesn't bite very often, and she has never broken my skin nor left a welt.
Pionus are much less active than green cheeks, and quite a bit less active than poicephalus. They are happy to just hang out with you. Daisy is older, so baby pionus are probably more active than she is, but Daisy can be trusted to just hang out on the back of the couch for a while and she won't tear up things, while all of my other birds need lots of toys to prevent them from tearing up my things. Daisy eats a little bit more than Roni, but she goes through toys much less quickly, so I think, if I really kept a log, that she doesn't cost me more to maintain, and she might even cost me less. I've never been bitten by a pionus, but I suspect it would hurt. Pionus will learn tricks and such, but they don't take to it as quickly as green cheeks and poicephalus.
The only other advice I have to offer you regarding both pis and pois is that they really need to have their cages against at least one wall to feel safe in their cages, and they won't be happy until they feel safe. Shira, my green cheek, has no problem if her cage is in the middle of the room or next to a window, but both Roni and Daisy need to have a wall on at least one side of their cages, and they are happiest in corners.