It is good to have a favourite one.
tbh not really. You need at least 3-5 depending on what they are good at because one person can say something in a certain way and you get it even if it's said by another person, the exact same way. Also once a reader knows you and your situation, from my experience they stop giving you psychic advice and then it just becomes (advice). You will want them to tell you things you don't know, not what you already know, although it's good to get confirmation that they are reading for the right person. It's annoying and once/if you drift over that line of being friend(s)/friendly (or so you think), they will start talking about themselves more and not leaving or allowing more time for you to talk about why you called. Some do this right from the beginning though.
You should also know your preferences of what type of reader works for you. There are more tarot readers out there than anything but it doesn't mean they are psychic nor are they intuitive. Many people pick up a deck of tarot cards and say they know how to interpret. Empaths (there are a ton on Keen), can be very accurate but they primarily only give you what they are currently picking up and as soon as you get off the call those feelings/images can change. Yep that quick. Readers who use tools are not specifically an issue, just make sure they are intuitive. That seems to be key, again in my experience.
If a reader has their own private site, choose the cheapest option for a reading and if you feel like they did a good job then wait 3 months then get a longer read the next time. Also, search for them to see if there are other places that may provide cheaper options (etsy, fiverr, reddit, youtube, FB, etc). Some readers you can book within a week or 3 days even, but for others it will be two weeks out or more.
I'm not saying to binge but you should have a handful to call on just like a list of vendors, that sort of thing. Also, no reader is 100%, this is said often on this forum which means the reader is going to give you things that are correct and they are also going to say things that are flat out wrong. It's up to you to decide if it is worth it to keep paying them and try to never forget **you are a paying customer and the reader is supplying a service.