Whether you're a beginner or an experienced tarot card reader, there are literally hundreds of ways to choose a deck. It can surely be overwhelming. However, if you go through all the methods to choosing a deck, they all ultimately can be boiled down to two: visual and intuitive.
If you're primarily a visual person, your choice of cards will be driven by their appearance or theme (e.g. Angels, Fairies, Celtic). On the other hand, if you can feel a connection when picking up a deck then this could be a decisive factor in making your mind. "I feel like this deck is for me", you might say.
Whichever method you use to choose your deck, make sure you get the full 78 card deck with illustrations that are easy to understand and the cards are of decent quality (made to last you years). The size is important too, to match your own individual hand size as you don't want a deck you can't comfortably shuffle. A good start would always be the Rider-Waite deck. It is the most referenced deck by Tarot guide books and has a fairly easy visual system to learn. A perfect starting point for a novice reader.
In the most important ways then yes but at the same time they are all subtly different. While the types, number and meaning of cards remain the same, the illustrations can vary greatly. Because of this, the differently illustrated cards may have a different meaning or "resonance" for you in a reading as opposed to the same card from another deck. For example, a card representing a strong and dominant man in the traditional Rider-Waite deck may signify an oppressive or controlling force, whereas if a different deck expressed the same figure illustrated as a young woman then maybe the reading is telling you something else - maybe a sign of "tough love" or being cruel to be kind.
Some decks use Christian symbols, others lean towards paganism. Some express mystical, African, Asian or Native American motifs. Decks like the Universal Tarot mix illustrations from different cultures and traditions.
Whichever deck you chose it is important you are aware of the symbols it represents and are comfortable with the overall feel and look. If the symbols used don't hold any meaning for you, then you won't be able to intuite your readings.
Similarly, find a deck that focuses on the areas of life most important to you. If you want to divine answers on your love life and romance, pick a deck that speaks to your heart. If you want to know more about your future finances then pick a deck that you feel oozes a sense of wealth and riches, and so on.
Before diving further into the topic of how to choose your deck, first I want to make one point clear. All the talk around the myth that you can't buy your own tarot deck is just a myth. Not only you can buy a tarot deck for yourself, you also absolutely should pick your own as it's a deeply personal thing.
Tarot cards are a tool to help uncover the inner truths about your life and can provide guidance on certain life's choices. And as with any tools you need to know how to use them and be comfortable using them. Especially with the visual features of the deck. The ability to easily interpret the cards can't be stressed enough. In some decks it is not immediately obvious whether the card is upright or reversed.
Look at several options, get a sample pack, try and see if you're comfortable with it.
Below is a list of recommendations I would give to anyone wondering how to choose their deck:
If you have a New Age shop in your neighbourhood, you should definitely start there. The shop staff will most likely have sample decks for you to rattle through and can offer a piece of advice. Get a few decks, look at the illustrations, see it they make sense to you, if you can find some meaning in them even though you can't yet interpret them into a full reading. Feel the cards and see if they make a connection with you. If somebody told you to get a particular deck and it does not appeal to you then get another one instead. Keep looking until you feel the connection with the right deck.
To find your local store, you can google "local new age shop", or "psychic, mind, body and spirit shop near me" and see if you get any results. Alternatively, you might be surprised to hear that you can also checkout pretty much any book shop. If they sell books there is a good chance they also sell tarot cards.
Another place to look for your new tarot card deck is a specialised online tarot store. And once again google search is here to help you find places that sell tarot online. For example:
Ebay, Amazon, Etsy, etc. - as expected these are also some of the places you can find tarot decks.
The short answer is it depends. It depends on your situation first of all. If you're new to tarot card reading, go with Rider Waite as it is dead easy to follow and there are tonnes of tarot books out there referencing this deck.
Once you're comfortable with that and you feel you want something more tailored to your individual personality, then you can go onto exploring the multitude of decks out there.
If you want something a bit different than Rider Waite and you have been in the world of tarot for a while, my advice would be to try to find an actual place that sells tarot cards as opposed to buying online. Go there, get a few samples of the cards. Find the illustrations that you're most drawn to and see how you feel about the overall theme. There is no better way to choose the right tarot card deck than in person. Then afterwards go online and buy it cheaper.