Oh boy. This one is enough to make my head rupture. So many candidates so where to begin. Well I'll begin by picking out a top 5.
In no order: Rondo of Blood, Symphony of the Night, Aria of Sorrow, Dawn of Sorrow, Circle of the Moon.
Just missing the cut: Order of Ecclesia, Portrait of Ruin, Harmony of Dissonance and to a lesser extent bloodlines.
So now I'll work off that top 5. Hard to find any weak link in that lot. First to go would be Rondo of Blood. Great game, but I think a tad under the others here. I'd put Aria of Sorrow and Circle of the Moon both in the next group. Both fantastic games but we are splitting hairs here. So it comes down to SotN and Dawn of Sorrow. A top 5 PS1 game vs the best DS game ever made (imo). Both are in the all-time greats category. In the end I gotta give the final nod to Dawn of Sorrow. I actually thought the use of the touch screen was great in the game.