I don't know much about dignities, but maybe this could help. Go to astro.com and click on "Horoscope Drawings & Calculations". Then click on "Extended Chart Selection" and select "Pullen/Astrolog". Look for "Sign/house dispositor graph" and click on it. You will be able to see what planets have the most energy in your chart. I will put mine as an example:
As you can see in the first graph, Saturn is disposing of all of my planets, except for Pluto. Saturn has a lot of "subordinates", while Pluto is rather a loner. This way i know Saturn is collecting the energies of all of the planets it's disposing of. But, since Saturn is not ruling over Pluto, i can't really say for sure what planet is stronger. At this point, what i can do, in order to break a tie, is to locate the ruler of my Asc and see which planet is disposing of it. The ruler of my Asc is Jupiter, which is disposed by The Moon, which is disposed by Mercury, which is disposed by Saturn. In the same way, we see that The Sun if finally disposed by Saturn.
We also have to take mutual receptions into account. In my chart, Saturn and Mars are in mutual reception by exaltation, which, in a way, means they are sharing their energies.
So to conclude, the most dominants planets in my chart are:
Saturn > Mars > Pluto
You can also calculate Lilly Strengths (based on essential and accidental dignities) by using an Astrology Software. This is what i got:
Saturn > Mars > Uranus > Pluto
Hope this helps ^.^