Both have similar offensive abilities (i.e they can both launch ranged attacks that are quite similar i.e the whole solar plasma/concussive thing).
However Starfire should take this for the following reasons:
StarFire: Can fire concussive blasts SunFire: Can fire solar plasma. Thus: Analogous
StarFire: Can fly (and very well) SunFire: Can fly (and very well) Thus: Analogous
StarFire: Excellent H2H combatant due to training by the galactic renowned Warlords of Okaara. SunFire: Excellent H2H combatant due to training in Japanese martial arts. Thus: Analogous (BTW when I say analogous I do not mean they are equal, but rather that they are equitable ......one may be better, but the other can still keep up in some manner and is thus now owned).
Now, here is where StarFire defeats Sunfire:
StarFire: Has amazing amounts of Super Strength that has allowed her to even trade blows with WonderWoman for a while. She is one of the strongest Titans. SunFire: Does NOT have the strength levels of StarFire ....or for that matter even approach it.
That is a major difference.
They may be analogous in the other areas ....from their ranged attacks to their excellent knowledge of H2H combat, but when it comes to strength levels they are not peers.
Thus that is the dilemma for SunFire ....how does he defeat someone who can do everything that he can, but who also has super strength added on top of that? She is everything that he is, and then more.