Are All Might and Midoriya equally strong when they use One for All 100%?
As @Ero Sɘnnin stated OfA stockpiles however with the latest chapters of manga we have to consider one more thing.

Manga spoilers:


   In the latest chapters in his dream, Izuku sees the first user of OfA, brother of AfO user, and some event that happened at that era. However at the end first user of OfA talks with Izuku. That never happened to All Might and this is stated in anime and manga. After waking up his hands starts to glow. I think that was a power-up so he is definitely becoming stronger and will suppress All Might.


Not the mention of he calling himself "Greatest hero" in the first episode.