There is an updated DDR A3 Difficulty Tier List powered by data submitted to 3icecream that ranks all songs by subdifficulties relative to each other. Songs with a certain level are broken down into different tiers, marked from X.00 to X.95 (X.0 to X.90 for Level 17-19). The higher the song is in a tier, the harder it is to score on.
The subdifficulties are calculated using an algorithm which considers score data submitted to Sanbai Ice Cream. The algorithm compares pairs of charts; for each pair of charts A and B, if more players have a lower score on A, then the algorithm will place A in a higher subdifficulty than B.3icecream