¿Porque no los dos? https://en.wikipedia.org/wiki/Liquid_rocket_propellant#Bipropellants https://en.wikipedia.org/wiki/Liquid_rocket_propellant#Bipro... edit:

¿Porque no los dos? https://en.wikipedia.org/wiki/Liquid_rocket_propellant#Bipropellants https://en.wikipedia.org/wiki/Liquid_rocket_propellant#Bipro... edit: I found people that tested the pentaborane/fluorine combination specifically, https://apps.dtic.mil/sti/trecms/pdf/AD0270941.pdf https://apps.dtic.mil/sti/trecms/pdf/AD0270941.pdf ("EXPLORATORY RESEARCH ON HIGH ENERGY PROPELLANT SYSTEMS" (1961)) - "An instantaneous hypergolic ignition occurred with a very long brilliant greenish-white flame and clouds of dense white smoke. Approximately four seconds after the start of the run, a leak developed in the fluorine valve stem. The lowered pressure in the fluorine line caused a flashback and the fluorine line ruptured. The very fuel rich combustion and decomposition of pentaborane which then resulted quickly plugged up the injector holes with the thick polymerized products of decomposition of pentaborane."