Speculah:Mami is the Strongest Theory

Mami's relative strength is a point that has been argued among fans many times. Here is a chart showing the evidence supporting and against the theory that Mami is much stronger than the rest of the cast.

Mami is normal	Mami is one of the strongest
	Mami can be considered to be the second most powerful magical girl in the mainline series, an observation which is easily backed up by the casual and cool attitude she adopts when engaging in witch hunts. This is also supplemented by her near perfect accuracy (scoring a perfect hit on Charlotte's small body at a distance), extremely quick draw (clearly shown when battling Charlotte's minions), the potency of her magical bullets (killing Kyoko with a single shot) and the sheer raw power of her signature Tiro Finale finishing maneuver. In fact, there is speculation that Mami could potentially be the most powerful magical girl to exist in the mainline series if not for Homura actively mucking around with time and giving Madoka a huge amount of cosmic karma in the process. Interview with Urobuchi Gen, as well as the dialogue between Sayaka and Kyubey in the episode 6 of the anime and the manga seem to give support to the idea that Mami is the second most powerful magical girl in the main series. However, it should be noted that they only refer to each of the member's 潜在能力　(potentials), and thus it is possible that other members, through training and experience, may be more powerful.
The idea that Mami is the second most powerful is up to debate. In the Drama CD "Farewell Story" Kyoko displays a brutal strength superior to that of Mami (albeit one can argue that Kyoko's brute force makes up for her lack of style and strategy). While it is true that Kyoko was defeated in Episode 10 with one single bullet to her Soul Gem, we must take into account that Mami caught Kyoko completely off-guard. Such act would display that Mami is a skilled shooter and quick minded, but it says nothing regarding her measure of power or strength. Nor one can make an argument that the ease of destroying of a Soul Gem is evidence of superior power for there is not enough information to determine the fragility of Soul Gems. In fact a normal bullet from a normal gun can shatter a Soul Gem as demonstrated in the Oriko manga Volume 2. So it is possible to suspect that a Soul Gem will remain equally fragile to other soul gems regardless of the strength and power of the owner. It is suspected that Mami's laid back attitude and her friendliness can be attributed as a weakness that caused her defeat in Drama CD "Farewell Story" and her carelessness in Episode 3.	Given the situation, it is difficult to assess whether Mami has fought at her full strength in her battle with Kyoko. Also, a fight between magical girls may not be the best way to measure each of their strength, as their fighting style, abilities, and magics are diverse enough for it to give significant advantage/disadvantage depending on the match up. For example, Kirika's slowing abilities are devastating against Mami (see second volume of Puella Magi Oriko Magika), while Homura's time manipulation is useless when tied up in Mami's ribbon (episode 3 of the main series). It has also been noted that though Mami has great magical potential, the magical ability given to her by her wish (the ribbons) is not suited for combat as opposed to other magical girls (such as Kyouko's Rosso Fantasma, Homura's time manipulation, and Sayaka's super healing). Thus, she chiefly uses magic she attained later on, and may not have been as powerful of a combatant in the past.
Additionally, in episode 10, timeline 1, Mami herself says that Madoka may soon eclipse her as a Magical Girl. She could be trying to appear modest, but this is reinforced by the reality that Mami did not survive the initial encounter with Walpurgis Night, while Madoka did. Regardless, it is indisputable that Mami is one of the most seasoned / "elite" (Oriko Magica) of the Magical Girls encountered in the series.	There are degrees of strength and power that can't be easily measured given the diverse nature of magical powers in different girls. It would be more accurate to say that Mami is the most experienced magical girl, but not the most powerful.
	In the fight between Homura and Mami, the two are equally matched until Homura decides to bluff shooting herself in order to catch Mami off guard. It works and she manages to sever the ribbon connecting Mami to Homura, thus freezing Mami in time. However, this too was a decoy by Mami, who once again bound Homura. This doesn't say much about her power other than she is able to keep up with Homura when it comes to speed, precision, and agility, and that she is able to effectively plan ahead based on what she knows of her opponent. Still, Sayaka berates Homura after the fight and their following escape, telling her she was foolish on taking on Mami's "Peak Form". Considering, at that point of the story, that Sayaka knows just as much, if not more than Homura, about the events occurring in the "world", gives Sayaka's opinion on Mami's power that much more credence.