Best of both what? Surely the only point of hold ups is that they supposedly don't need a suspender belt? If you attach them to a belt then surely you've just turned them into a pair of stockings with an uncomfortable sticky ridge on the top.
I have never in my life got any hold ups to hold up, including M&S. They are fine as long as I'm not moving. As soon as I start to move, they just unroll. My thighs are fucking massive though.
I use both. "The best" is that the suspender hides my tummy. If the stockings are actually pulling down on it, it has to be tight to stay on my waist- which creates its own squish problem. Hold ups stay in place, so no pulling down. A medium suspender looks best on me, but it takes a small if they have to do any heavy lifting.

Maybe you're buying stockings too big if they're rolling down. If you're going larger so they don't press in and make a line, try a size smaller, put them on, warm up the sticky band with a hair dryer and smooth it just right. Then let them cool and take off. I do that with mine because my legs aren't big, but they're definitely...soft.

Oh and wide lace tops are much easier to stretch/smooth this way than the regular bands. Dunno, may be worth a try.