The right tarot deck for a reader is one the reader would be comfortable looking at for extended periods of time. If that is the very popular Rider-Waite-Smith deck (also called the Waite-Smith deck), then so be it. If the reader prefers the International Icon Tarot, then this too is good. If the reader is fond of American 50’s aesthetic then the Housewives Tarot would be a welcome study partner. There is no one deck that all tarot readers are required to have.
Tarot readings as cartomancy and divination started with a deck of cards that was used for playing the game of tarocchi. The images portrayed on those first cards were relevant to the players of that time. When the field of cartomancy became a lucrative business, various writers attributed meanings to card symbols that were initially decoration. By the time tarot decks were published explicitly for cartomancy, the number of symbols on the cards had multiplied, along with the various meanings and attributions that could be assigned to them by the knowing and unknowing alike.
As the number of pagan, neo-Wiccan, non-Christian, and non-religious tarot readers increased, the market responded to the unfilled desire for tarot decks that were absent of the Christian and European imagery that were the face of tarot cards for centuries. So-called “novelty” decks were printed and bought, each one designed to fill a certain niche. Instead of angels, there are now fairies. Instead of a pope, there is now a god of wisdom. Cats abound and woodland creatures proliferate. (And yes, there are dragon themed decks.) Some decks have done away with scenes, returning to pip-only cards. A few decks have abstractions instead of anything quickly identifiable by sight. All they share with decks a generation before is the title and function of a tarot deck.
But for all the alterations and changes, a tarot deck is still just a tarot deck. Just as there is no one true way to read tarot, there is no one true tarot deck that must be used. Because of the ubiquity of the Rider-Waite-Smith deck, it is used as the default deck for courses and discourses on tarot. It has become a common point of comparison.
If your personal path requires you to use a particular tarot deck, then that deck is the right one for you. If your personal path requires you to avoid or abstain from certain themes, authors, and/or techniques, then by all means, abide by your path. But do not think that you must have a certain tarot deck to be regarded as a “right and proper” tarot reader, or that you must read cards by a certain technique for the same. Once you choose your deck, be consistent with how you read it. The meanings may drift over time as your understanding increases, and you may see symbolism where the artist did not intend, but that is a private conversation between you and your deck(s). The right tarot deck is not one that was gifted to you in accordance with superstition, not one that the popular books say you must have if you wish to be serious about cartomancy, and not one that is off-putting or makes you uncomfortable to view. The right tarot deck is one that you are comfortable and happy with. And if it happens to be covered with happy little cows, then moo on with yourself.
An extensive list and reviews of tarot decks can be found at Aeclectic, but be warned, that website is a time sink and will make your budget cry.