I've had five decks, but one went missing. The missing one is the standard Rider-Waite. I got that one first to initially learn how to use tarot because my uncle had already given me a book on them. They were very useful at the time to learn, but after a while I realized that they were not really for me.
I then got the Russian Tarot of St. Petersburg. These ones are really quite nice to me as they have a black background and a golden border. The images are colorful. I use these very rarely anymore.
I also have the Gothic Tarot which has really dark images including vampires, succubi, spirits, gargoyles, etc. Very nice cards. I still use them once in a while.
I have the Crowley Thoth deck and accompanying book. I haven't finished the book though yet. I kind of stopped in the middle because alot of things came up all at once, and I haven't gone back since. Though summer is coming, so I'll probably have more time then. The cards are very interesting with their imagery and symbolism. I use them still.
My favorite deck that I use the most is the Sacred Circle. It's absolutely beautiful. Some of the art is computer generated, but the pictures show natural scenes. The cards are nice and big too. And I love how the borders are different and correspond to each of the elements for the minor arcana.
http://www.aeclectic.net/tarot/cards/sacred-circle/
I was looking at some of the decks that other people mentioned, and I really like the Shakespearean decks (there were a few) because of my enjoyment of Shakespeare, and the Cosmic Tribe tarot has really intense images and kind of gives the impression of a dream or a "mental trip" and I like that. Also the three lovers cards sounds really interesting since I'm really open to things like that. Though I always saw the male/female lovers as symbolic of energies rather than physical gender, I think the three lovers cards are an interesting and innovative idea.