I have yellow napes and have bred them in the past. Females are generally the easier sex. They can be pretty spicy, but usually not super difficult. Males are much more likely to launch themselves as you and attach to any body part they can reach with their beak, dig in, grab another chunk, dig and and repeat until you scrape them off you. Females are more likely to have a definable trigger. Often that trigger is some unliked thing approaching their favorite person, in which case they will bite their favorite person. My older female nape came from a family with a grey. The grey was there first and she made him nervous so they rehomed the nape. They can be aggressive toward other birds. In my experience, the females are at least as bad as the males if not more so toward other birds. Actually, my pet female nape just got her toe bit tonight when she flew to her sister's cage. Sister didn't think about it a second, lightening fast reaction to drive off the other bird and bite. Thankfully not a bad bite though, but had I not been there, she probably would have tried to remove the toe.
The key to amazons is watching body language. Ask before touching and be willing to accept no for an answer. Walk up to them and just chat with them for a bit while you assess body language before asking for a step up. You can avoid A LOT of bites that way. Learn your bird's triggers and they will become easy to avoid. My amazons are all triggered by dogs. I have to be careful when there is a dog around because if the bird takes exception to the dog while the bird is on me, I get bit. Sometimes they will take exception to their favorite person's spouse or kids in which case everyone needs to learn to back off while you hold the bird.
Another key to amazon success is don't try to hard to make them like you. It gives amazons the heebee jeebees. In other words, they will think you are a creeper and try to get rid of you. Stop for a moment when you walk past their cage a few times a day. Ask if they want a scratch, wait for them to say yes with body language, give out scritches for a minute or two and then go on with your day. Don't think they actually want to spend the next two hours attached to you because they probably don't. And trying to convince them to sit with you for more than a few minutes is a fast way to teach an amazon to bite. End all interactions on a good note before the bird decides she's had enough of you and bites to make you go away. If you ask the bird if she wants to step up or get scritches and she turns her back to you, growls or just seems uninterested, consider it a NO and go on your way. Don't take it upon yourself to pester her into changing her mind because they you will just be cramping her style, she will resent you for bugging her ALL THE TIME and start biting first just to make you go away. Think teenage girl behavior or cat behavior. A light touch and plenty of space gets you more than chasing them around trying to be their friend.
I really enjoy my amazons. I think my females are nearly perfect. But, I don't blame them when they make me bleed. I blame myself for not seeing the signs. And, I have other pets, so its not important to me that my amazon want to sit with me for hours on end.
Many weanling baby napes go through a very trying full pressure biting stage. I believe this is a big independence stage for them where in the wild they'd be flying like crazy to work off energy. Around the house, they have a human constantly pushing hands in their face and trying to sweet talk them into interacting and holding still and being petted. Some people have a difficult time with those full pressure bites. They rarely make you bleed by OMG do they make you hurt. Babies do eventually work out of that phase, but sometimes it can take anywhere from a few months to a year. Depending on if you try to train it out of them, mess it up and teach them to bite just to get rid of you so they can go play on their own which is what they really want to do. If you just leave them to be an independent baby, keep interactions short, and don't give them a chance to bite you, don't get your feelings hurt when its been days and the bird hasn't asked for a scratch, just give the bird space and chew toys, they will eventually grow out of it. Although it may seem at times like the bird lives there and you don't really have a relationship with it. Things will change when it grows up. Although even adults can go through independent stages where they like you, but they'd rather you not touch them. My female has been known to go through 6 weeks at a time in December where she really acts like she could care less what happens to me. Then after a few weeks I notice she's leaning forward and giving me body language like she wants a scratch and just like that we are back to being friends.
Personally I think they are a good species for people with other pets or semi busy lives that have some time for a pet, but don't have time for a soul mate type of pet. The amazon will certainly act like it likes/loves you at times, but they have other things to do that doesn't always include you. Sometimes sitting around and thinking about taking over the world is way better than dealing with an actual live human being. And you can see when they are thinking such thoughts. Their tail will twitch to a half flare and their eyes will flash for no particular reason. Usually that means if you try to hold them, you will get bit.