Wow, the majority so far riffle shuffle!!
All my 21 years in Tarot, for some strange reason, it's never occured to me riffle shuffle. I do playing cards, in fact, because of my dad I have quite the many fancy card shuffle methods (he did card tricks and magic).
Perhaps because to me Tarot cards are on a different level, a whole other realm to me. I shuffle as a meditative, relaxing practice as well....to feel the cards, caress them lovingly and infuse my energy and being into them.
And riffle shuffling would just damage and cause such wear and tear on my cards in shorter a time, imo.
But I think it comes down to respect. Because I grew up with tons of card games, card tricks....just playing around with them, that when I got involved with Tarot....they just were so different to me than playing cards that I couldn't treat them the same way.