When it comes to someone new and just learning the Tarot I will encourage them to start with the Rider-Waite deck because of its simplicity. There are a few others that fit this same standard but I think they look a bit cartoonish. The thing is, you will find more written material using this deck as a primer than most any other out there. Start with it and the Eileen Connoly book series (
http://www.amazon.com/Tarot-Handbook-Apprentice-Classic-Connolly/dp/0878770453 -- the starting point)
Once you're comfortable with these foundations, then you can start exploring other decks, finding the one that "speaks to you". I don't mean that in some esoteric way but more on how you are drawn to the deck and the ease by which you are able to "read" the cards. Let me explain a bit...
I use two different decks for two different types of situations; the primary deck I use for regular Readings is "The Old Path" Tarot. I use it because it is full of symbolism that allows me to "layer" the Reading; herbs or other plants in the background, colors, etc. are all keys that aid me in divining what each card is trying to say as well as better seeing what the over-all spread is trying to convey.
The other deck I use is the Ancient Egyptian Tarot but I use it when the client needs to focus on "issues". The artwork in this deck is simpler and less cluttered than the Old Path deck -- more "neutral" if you would. Because of this I'm able to work with the client in ways that aid them in solving the road blocks or personal short-comings they're dealing with.
Finding a deck that talks to you in these ways -- the artwork being akin to a cue card that triggers your memory -- is where you'll find your strength. But too, if you should move deeper into the Reader's work, finding decks that can be used to aid your clients on deeper levels, such as I do with the Egyptian Deck, delivers even greater benefit; especially if you look at how this contrast affects the client psychologically -- the new and different deck making the session "special" and obviously different from the standard Readings they've gotten from me before.
As Mark has already pointed out, you will sometimes fall in love with a deck that eventually goes out of publication for a while. It can be rather frustrating

That is why I made certain I had several copies of my favorite deck when they came back into print.

Sadly, there is still one deck that I absolutely love that still hasn't come back on the market and the almost 20 year old deck I have left really needs to retire. The deck I speak of isn't a Tarot deck but based on Bibliomancy; something I think most magic types would enjoy using because of how it is structured. They call the deck "ABUKERA" and I can assure you that it comes in handy on those long days working festivals or Psychic Fairs... far less burn-out!