I would always advise a person to choose their deck by what art appeals to you because we all have different tastes in art, so if you like the deck, that opens the way for you to get more familiar with it and see more into it. By that I mean that if you enjoy looking at it, you notice many things about the design, the details, the expressions, etc. If you think a deck is ugly you don't even want to look at it much. When you like a deck you notice that the art really speaks to you and helps you give more fluid readings, more insightful readings.
Since I have a large collection, I enjoy using different decks at different times, although I have a few that I go to most often. I find that readings are influenced by whether one deck's art is very romantic looking or whether another deck is more abstract, or whimsical, grotesque or another is more blunt. They do influence what words come to mind, which of course then, affects the way I present the reading.
Some decks are such obvious RWS clones that even with different art, you have no trouble interpreting, but other decks are so radically different in their design that they demand to be handled differently.
There is not one best deck, but there are better decks for each person, depending on taste.
I am a professional reader, and I place several decks on my table and let people choose which one they want their readings with. I have noticed some surprising things.
This past weekend, I read at the Witches Ball and one of the choices was Deviant Moon. It did not get picked once. Tarot of Dreams got picked most of the time.
Yet at other metaphysical fairs Deviant Moon may get picked more frequently as well as Victorian Romantic and Old Path. Tarot of the Stars seems to get a lot of action some days and none on others. I take different decks out to play all the time and it is surprising sometimes what people pick.