Dohnanyi excercises are the only ones I practice - they are immensely helpful, but only if done correctly.
Any way you do them, you are creating muscular pulls, and will eventually injure yourself. There is no "correct" way of doing these, and ultimately you are just wasting your time. After skimming through posts, I see "bernard" has said many wonderful things on this topic, so I'll stop right here.
If you think piano playing has anything to do with "building finger strength", then you're in for trouble.
If you really want to practice exercises, stick with czerny. You'll end up with not only a technical skill, but a short piece of music as well.