I know there are a lot of blog posts about this already. Most of them will tell you to find a deck that “resonates” with you or give you a list of a few good options. I, on the other hand, have a much simpler solution. Just get the standard Rider-Waite deck as your first deck.
The reason for that is that it is the classic deck and it still has the esoteric symbolism in it that is lacking in many more artsy decks. It is also the most used deck in the world and most books, articles, videos etc. will be using this deck when teaching tarot. So when using this deck there is always a lot of source material that you can refer back to. That is not the case with most other decks so it can be very difficult when you are left alone with a short booklet and images that no longer holds the esoteric wisdom in them. Chances are therefore that, if you choose another deck, you are more prone to get stuck and therefore give up more easily.
The Aleister Crowley Thoth deck is obviously an excellent deck, but I wouldn’t recommend it for beginners. It certainly is rich in symbolism and it even corrected some mistakes in the Rider Waite deck, but for the most part, to most tarot readers, that isn’t going to matter all that much. If you are heavily into the kabbalah and pathworking and so on, you will need to know about this though. It is probably the deck with the second most material published though. Just be prepared for quite a challenge and a lot of motivation if you start out on this one.
The main strength of the Rider-Waite is that it also has the minor arcana painted with imagery that will give you clues to the “meanings” of the cards. The Thoth deck is a lot more abstract and therefore more difficult to start with.
Having that said, if you get a second and a third deck your choice is going to be a lot harder. Then you can go with whatever you prefer. I have gotten some decks just because I like the artwork. In those cases though, I still use my Rider-Waite knowledge when using those decks. I don’t “learn” a new deck. I use what I already know and and all I have done with the new deck is that I have substituted the physical images. Sometimes they can bring new ideas or perspectives to the table, but when you have that Rider Waite base knowledge you can always return to that and be certain that “everything” is there. If you go for the Thoth Deck I would consider relearning a few things though.
There are some exceptions of course when choosing a deck, for example, if you are taking a course which is recommending a particular deck. I did that myself, but that course wasn’t focusing on the tarot for tarot reading, it focused mainly on the major arcana for contemplating sessions. It was excellent for that purpose, but when I wanted to learn how to do proper tarot readings the minor arcana cards in that deck were too abstract, so I still ended up with having to switch my deck to Rider-Waite when I wanted to learn regular tarot reading.
-Thus spake the Night Spirit