Mummy, Gringotts, FJ, MiB, Spiderman, Transformers - all short if running. Especially MiB. That is always walk-on IME. The others are most often under 5min. I only found RRR to have a consistently longer single rider wait. (Have not done Hagrids or Velocicoaster as single rider - I assume they're a bit slower like RRR, since those are all the 2-seater coasters so fewer single open spots available.)