I'm probably going to get downvoted for this, but like it or not, this is what has worked for me.

I've tried Czerny, Dohnanyi, and Liszt. Dohnanyi is the most concise set of exercises I've seen, and Liszt is focused and comprehensive. Czerny's just all over the place.

I'm an adult who works full-time, so I don't have the luxury of being able to spend all of my time playing scales and exercises. When I was going through Liszt and Dohnanyi, my focus was to play the exercise correctly at least once at a tempo as slow as necessary, especially for the finger exercises (don't want to play these too fast - you may injure yourself). I tried to take Czerny seriously, but couldn't. These days, I just use Czerny for sightreading practice.

All of this said, I don't spend that much time trying to perfect these exercises and etudes. I've found that I learn best by concentrating on non-etude works - i.e., repertoire that I actually want to learn - and gradually build up the difficulty.

For this reason, I don't practice my scales. Again, I'm an adult who works full-time and my time to do things aside from my job is short. I know theory well enough to be able to tell you the notes for the major scales, all three forms of the minor scales, arpeggios (major, minor, dominant seventh), how chords are formed, what modes are, etc.. I know how to finger major scales. But I don't find it worth my time to be practicing all three forms of the minor scales, all of my arpeggios, all of my whole-tone scales, all of the modal scales, parallel and contrary motion versions of these... there are just too many possibilities, and I find that in practice, scales are rarely very useful.

Rarely do I find myself (at least currently - I've learned the Chopin c# waltz and the Rachmaninoff c# minor prelude most recently) in a situation where knowing a scale would've been useful. Hence I don't like a lot of Czerny (School of Velocity, I'm looking at you).