I use both. In the weight room when I want to hit strict numbers I use %s. However on the track I will usually up or down regulate depending on what I see. Later in the year I’ll often use RPE for intensity because it’s a way of introducing a little bit of autonomy and auto-regulation in to the program. This really only works best with athletes who know their bodies well AND who aren’t OCD about training (and want to hit numbers regardless of how they feel).
Research evidence suggests that RPE values correspond VERY well with actual % intensity markers.