I was asked a question on how I choose which tarot deck I use for readings, which I thought was a great question because it isn't something I've really thought about doing, but just do. Short answer is: I go with my gut.
Currently I have about 13 different decks to choose from. Of those, I actively use three. Two traditional tarot decks and one oracle deck. I am a bit of a collector and prone to "shiny!" grabby-hands impulse tarot purchases, especially if it is an independently published deck. There are so many people out there creating really cool decks right now.
I have a very deep bond with my Smith-Waite deck. It was the very first deck I have ever owned and we have done some serious shit together. As a result, this is my default deck, the old trusty friend I can always go to and know I'll get a solid unwavering answer from and I know that when I read for others, the same applies.
The second deck I work with I feel is a more nature, pagan and witchy version of Smith-Waite, so the suits translate fairly well between decks. They're similar but not the same. I often go to this deck when I am dealing with more wild, green and witchcraft oriented situations. It's also a great deck for me to understand my dreams, as I dream often of plants, animal and wild places.
Third being the Earthbound Oracle. I really like this as a supplemental deck to draw on for tarot readings. To kind of back up another card or use as an action card, or energies surrounding the situation. A good example is how I used it for my Samhain spread.
When it comes down the choosing a deck for a reading it usually goes something like this:
*sits at table and stares at decks for a while, while contemplating an issue, question*
*knocks on table three times, has conversation with familiar spirits, gets feels*
*looks at decks again*
*picks deck giving good feels*
Hah. It really is hard to describe. But I feel that each deck contains its own spirit and depending on what I am needing to read about, or on, it will reach out to me. And they do, every single time.
So if you're all starry eyed and deck lusting as one does when one loves tarot, I would pick one deck that sits close to your heart. Study and work with it daily, then pick another deck that you're very attracted to to act as an alternative and go from there.
Another useful trick is the good ol' pendulum! I employ this when I am reading for clients. Actually, especially when I am reading for clients. I set both my RWS and Wildwood decks side by side and while holding the pendulum, I state, "who wants to read for Brunhilda Birchswitch?" (I made that name up, I don't know where it came from). And 100% of the time the pendulum swings one way or another and the deck is chosen. If you wanted to apply this to a personal reading just ask, "who wants to read for me?"
Another angle to approach this is knowing your deck. Decks have personalities of their own and I can tell you that I have experienced some decks getting snarky because I haven't used them in a while. Yes, I am looking at you RWS. Conduct yourself an interview! Ask your deck what areas of life it specializes in, what situations it works best in, how you can best read with it. That can help you in knowing when to choose the right deck for the right situation. Or just giving you a better feel for the appropriate time to use it.
Above all though, don't think too critically about it. Go with your gut feeling. If it feels right, it more than likely is! Trust the process.