Endeavor and Dabi seem to have very similar quirks, with the exception that the flames Dabi generate are blue. Is there any other difference? Is one quirk stronger than the other in some way?
Both quirks essentially do the same thing, but blue flames (used by Dabi) are hotter and more fuel efficient than red flames (used by Endeavor) though Endeavor uses blue flame as special move while all of Dabi flames are blue.
Because blue flames burn oxygen more efficiently, Dabi can create big attacks with less effort than Endeavor.
In my opinion Dabi quirk is more stronger than Endeavor quirk.
For now it's just speculation (manga reader) but there is a high possibility that Dabi is the son of Endeavor. As manga and anime stated Endeavor tried to create best quirk even one to exceed All Might. Fan base speculated that Dabi is one of his failed attempts.
We know that Shoto Todoroki has two older brothers. We see one in the latest chapters of manga. One is still unknown.
Left eye colour of Shoto Todoroki and Dabi's eye colour is same (Turquoise). Also, Endeavor's eye colour is Turquoise too.
As for the question itself they're both fire based Quirks, but strength wise, it's same. Colour difference is because of incomplete combustion (blue).