I always start with all the cards upright. I riffle, and if a small section of cards sticks and doesn't want to go back into the deck, I reverse those cards only, put them at the bottom, and continue shuffling. I do not force reversals, and they do not occur in most of my readings. When I was first learning the Tarot, I used to force reversals, but as my method developed I found they were not necessary to accurate interpretation. Since shuffling my way severely restricts reversals, they are very meaningful to me when they do appear.
After years of having the sitter shuffle, I now shuffle the cards myself and choose them myself. This has no effect on the validity or accuracy of the reading, but it does cut down on wear and tear on the cards, time spent shuffling, and sitters feeling self-conscious because they've never shuffled such a large deck, feel unsure of when to stop, worry that they're "doing it wrong," etc.