Choosing a Tarot deck is a very personal experience. While many believe that your deck should be gifted to you; I am one of those of a different mindset on this. Your relationship with your Tarot deck will become very personal and for that reason alone, I believe that you alone should choose your deck. While there is nothing wrong with having someone present you with a Tarot deck as a gift, sometimes it's just not the right deck for you.
If at all possible don't order your deck online because it truly does help to hold the deck in your hand and get a "feel" for that particular Tarot deck. How does it feel in your hands? How do you feel about the artwork? Does the artwork feel ominous of calming? How does it reflect your personality?
If you don't have a store near you that you can hold the cards in your hands then you do have many places online that you view many of the Tarot decks. One of the best sites I have found to do this is http://www.tarot.com/tarot/decks/index.php This site has many Tarot decks listed as well as the ability to view every card in every deck. If you must order online, make sure the merchant has a return policy. Before you take the cellophane off of the deck, hold it in your hand and see how it feels to you. If it doesn't feel right or good, return the cards and try again. It is not common that you will be able to connect with a deck later down the road, if you haven't connected with it from the beginning.
Many still love the original Rider Waite Tarot, but for others it appears just a little bit too scary or dark. This is still one of the most popular decks for Tarot readers as it has a long history and its meanings are pretty consistent with other decks. It is a good idea to at least become familiar with this deck if you plan on reading Tarot professionally.
Many Tarot readers have several decks, so when buying the deck, think about how you plan to use it. Is it for your own readings and guidance? Are you going to read for others with this deck? Who are the people you are reading? What kind of messages are you looking to pass along.
There are decks to suit just about any need. Some decks are more playful and childish, while others reflect strong masculine or feminine energy. Some decks are very spiritual and some are just fluffy. The choice depends on you as the reader and what you are seeking from the deck itself.
Be careful when choosing decks as not all Tarot are created equal especially when it comes to meanings. If you want traditional meanings then get a deck with traditional suit of Cup, Wands, Pentacles and Swords (Sometimes, the Wands may be replaces with Staves or Rods). There is nothing wrong with going with a less than traditional deck and always remember when interpreting the cards to follow your gut more than the rule book. You do not have to be psychic to read Tarot cards, but you do need to allow your intuition to have the final say in any reading.
That same intuition will guide you in choosing your Tarot deck, trust that what feels right by you and you can never go wrong.