Ralts, Kirlia and Gardevoir
Overview
Despite how elusive they may seem at first glance, the Ralts line was actually one of the first to be domesticated due to their resemblance to humans and is now fairly common in urban environments. They are not the easiest to raise due to their personalities, but they don't require much specialized care and are well used to living among humans. I have decided to begin with them and not with the Abra line due to me having more personal experience handling them, despite the latter being arguably more iconic.
I will not be talking about Gallade for reasons I will discuss at the end of the post, but as a general rule you can assume anything that applies to Gardevoir also applies to them.
Diet
They are omnivores and can eat pretty much anything, so common rations should suffice. They are not very well adapted to eating large quantities of meat though, so stick with berries if you want to go with something more natural. Any type of treat works for them, and in fact you should consider taking some time to let them try out all sorts of flavors and have them inform you which is their favorite.
Some sources say they don't need to eat and can simply live off emotions alone, but that is not true. Please don't starve your pokémon.
Handling
Ralts do not like to be touched very often, but they become more indifferent to it as they evolve. You may initiate physical contact if you have gained enough trust with them, but otherwise you will have to wait for them to come to you. They generally enjoy being pet on the head, though you should keep a safe distance from Ralts and Kirlia's horns (sensory appendages).
As a general rule, do not touch their sensory appendages. In some rare cases, Gardevoir may prompt you to do so to share something with you through telepathy, but that must always be initiated by them or given explicit permission if you have a really good reason to do so on your own.
They can bathe and feed themselves and do not require assistance. They are able to make use of most simple human mechanisms like faucets due to their humanoid body structure, just make sure to keep everything they need visible and within reach.
Behavior
Ralts are very timid, and will actively avoid you if they sense aggression from someone nearby. Wild Ralts tend to avoid those who are feeling sad, afraid or stressed, though urban ones are more tolerant to those emotions and may even try to cheer them up within their limited capacity. In general though, it's best to enter their spaces whenever you're in a neutral or good mood. An exception can be made if interacting with them makes you cheer up, as they really love whenever that happens.
Kirlia are less timid and will more actively interact with you on the daily. The stuff about emotions still applies to them but they are more tolerant to negative emotions than Ralts. They like to dance whenever they feel strong positive emotions nearby, and I recommend you watch them dance so you can strengthen your bond with them. Kirlia are also capable of creating visions with their powers, and will usually do so whenever threatened to buy themselves some time to flee. They may also do so whenever they have a request that can't be properly expressed by gestures. They can only make those with things that are already in the environment though, so you better get good at interpreting and riddles.
Elan's Tips
I like to place a bunch of pictures in Porcelain's space so she can have an easier time letting me know what she wants.
Gardevoir's behavior greatly varies depending on if they're wild or urban. Wild Gardevoir tend to be more territorial and somewhat aggressive, while urban ones are indifferent to pretty much anyone. Regardless, they can both form a very strong bond with their trainer. They'll often try to "protect you" from things that aren't actual threats, so you will have to be careful and spend some time training them on what to actually look out for. It's good practice to take fully evolved psychic-types with you on your daily routine and even give them little tasks to do, especially for pokémon that thrive off helping others.
And just in case you need to hear this: they cannot see the future, and they most definitely can't open black holes. They can use their advanced brains to predict the outcome of situations, and they can also learn Shadow Ball, which could be interpreted as a black hole if you have never witnessed it before.
Vocations
Kirlia and Gardevoir make pretty good service pokémon. They aren't naturally caring like pokémon such as Indeedee, but they are protective and can easily be trained to take less violent approaches on making others feel better. Kirlia tend to have a milder temperament, so I would recommend them for those who are younger or need mostly emotional and mental support. Gardevoir is more recommended for those with physical disabilities, since they have better precision with their psychic powers.
Elan's Tips
I don't want Porcelain to evolve, so I got her one of those everstone accessories from Eksy. I am fully convinced Meatgrinder is capable of making her just as paranoid as she is about Seviper if she ever evolved into Gardevoir.
Final Verdict
I'm not sure if I would recommend raising one of these pokémon as a complete beginner, but them being used to urban environments and not requiring specialized care is a big plus if you decide to do so. It might be tempting to get a Ralts and raise them from the very beginning, but there's no shame if you decide to start with a Kirlia (like me) or even a Gardevoir. They are very intelligent and well rounded once you get past their quirks, and they play nice with young and mild-mannered pokémon.