Sailormars is the Princess of Mars and one of the four guardians. She is the senshi that controls the flames and its power is useful against the enemies the senshi face.
"Kasei ni kawatte, sekkan-yo!" A force to be reckoned with. Sailormars is one of the Inner senshi and is said to be one of the most powerful senshi in the anime. This is based on the damaging power of her attacks and the information revealed in the series. (Her strength is also evident in the manga, however, as I am not as familiar here.) There are many debates of who is the most powerful among the Inner senshi, recently Sailorjupiter, Sailormars and also Sailorvenus are said to be contending for the position.
Go see her Attacks and Henshin phrases!
But I believe that each senshi contributes and there shouldn't be quarrels based on this. However, in some references in attack powers, it is said that Sailorjupiter's attack power is greater, and even Sailorvenus's attack. But inconsistencies remain. For one, in the episode against the last witches, Cyprine and Pikuroll in season S, Sailormars's Burning Mandala was dodged by the twin witches, and the damage was forceful enough to wreck an entire wall down. Sailorneptune once told Tuxedo Kamen that the Outer senshi should work alone, because not even Mars or Venus can handle their mission. There are still many elements referring to power and each variable can connote many things. And also by watching the series, we can note many inconsistencies that do not seem to correspond well to some references.
Basically, this is based on the information gathered from the series. There are people with credible background who do support this about Sailormars. This issue is not against Sailorjupiter and Sailorvenus or Sailormercury. (I like all of them, and besides, I'm related to the Kraiders who built sites for them) But should anything be clearer on this subject, I'll add on to this.
Sailormars fights with the Inner senshi and they always fight as a team. Their synergy and cooperation is really valuable and they usually talk together on their strategies. Only in the later episodes will they fight with the Outer Senshi more. Ready to go? "Henshin-yo!"