I use .75" or 1" and usually use stumps or slabs from the same batch of wood for legs. When using stumps, I use 3 dowels each leg in a triangle pattern. With slab legs I use three dowels in a row each leg. I might add that when using slabs as legs I use a stabilizing piece between them. Sometimes it's a shelf & sometimes it's just a nicely figured piece of wood to accent the table/bench.
Last one I built was black walnut live edge with slab legs also live edge. The stabilizer was birdseye maple. It looked great!!! There was a pith void in the center of the top where it was rotted away. I cleaned it out & filled with crushed turquoise then filled with epoxy. Once sanded smooth & finished, it glowed against the black walnut like a river running down through the plank. It was really cool. No pics though. I gave the table away to some family that was visiting for their new log cabin. Next time I visit them, i'll get a picture to post.