I use the Hitech filters in a Lee filter holder. The Hitech filters were cheaper and easier to get. I though about switching to Lee for a while already but can't imagine that the image quality would improve enough to justify the investment. The newer Hitech filters like the reverse grad NDs or ProStop IRND are also a bit better than my older grad NDs. A single Hitech grad ND or a Hitech grad ND + pol filter is fine. Two Hitech grad ND filters is not such a good idea because you may notice a tiny bit of haze caused by 3mm of additional plastic infront of your lens. But the pictures are still pretty good.
BTW, depending on the exact position of the Hitech reverse grad filter to the sun, a much more reddish picture can be the result. This is often quite welcome. The attached photo shows the efect quite well. Both pics are out of cam but resized. Half of the 2nd one was stacked up as a layer on the 1st one. They were taken seconds apart and differ only in the position of the reverse grad filter and shutter speed (1/15sec vs 1/5sec).
Best regards, Robert