Garrus Vakarian's character arc across the Mass Effect trilogy takes him from young, hot-headed C-Sec officer to a broken, jaded vigilante in the slums of Omega, before finally ending up as a Reaper advisor to his species and homeworld. All the while, he's always there for Shepard, following him without question even as they work alongside a known terrorist organization. He offers support while simultaenously taking advice. Once you pull Garrus away from those calibrations, his dry humor, awkward flirting, boasting atop the Presidium and other memorable moments make him a fan favorite. (So much so that players convinced BioWare to turn him into a love interest for female Shepard.) For all the friends, allies and other connections that the commander has around, Garrus is one of the stronger bonds and it shows. After all, Shepard couldn't do it all without Garrus - not as stylishly, of course.
Cyrus, Chrono, and Queen Leene will all agree that there is no friend more loyal than Frog. Frog was always loyal to Cyrus growing up, and when Cyrus became a knight, Frog (then Glenn) was his squire. Despite Cyrus encouraging Glenn to knighthood for his superior sword skill, he chose the support role. After Frog felt that he failed Cyrus in their infamous battle with Magus, he vowed never to fail anyone again. Despite his self-imposed exile, Frog was one of Queen Leene's most trusted knights and friends. Royalty is always surrounded by sycophants and conspirators, so a true friend like Frog is worth his weight in platinum. Frog found his redemption and faced his past through his emotional journey with Crono, becoming one of his most loyal and powerful sidekicks. Crono would be lost on his journey without a friend like Frog, willing to sacrifice himself for the honor of others and do everything in his power to make sure the people he's supporting succeed in their endeavors.