The other reviews focused on the anime, and I don't have much to say apart from how Girls und Panzer is a show that is well worth your time. This review deals with the manga, and the question of whether the same can be said for it.
The story is essentially the same as Girls und Panzer, although it's told from the POV of Yukari, rather than Miho. As a result, some crucial scenes are omitted or changed, whether the result of Yukari not seeing them (for example, Miho coming to Oarai and deciding to do tankery), or various other reasons, (for example, the first round shown is the second match with Anzio, rather than the first match with Saunders). As such, it's best if you already know the story before reading the manga.
Unfortunately, Yukari is largely a less interesting character than Miho, having fewer meaningful interactions with others. It's nice to see her thoughts, but it's unfortunate that most of them boil down to "I've got to support Nishizumi-dono!" The rest of the Anglerfish crew gets Demoted to Extra
, and develop far less over the course of the story. Oddly enough, even Yukari's own family isn't shown much, nor is her backstory expanded on apart from the part about her having no friends until she met Anglerfish Team. As such, I'm not entirely sure why Yukari was chosen as the protagonist apart from her popularity
, but Miho would have worked better as the protagonist.
There's a fair amount of information in the manga that can be quite interesting, shedding light on the tanks' capabilities, and on certain characters' actions. Unfortunately, the exposition can be ham-fisted at times, and tends to eschew the anime's tendency to Show, Don't Tell
. For example, we're told about the nature of Sodoko and Mako's relationship, rather than shown it.
Of course, this isn't to say that all the changes are bad. Some things are better explained than in the anime. Without spoiling anything, there's a change to Miho's backstory later on that provides an interesting possibility of why she was affected so much by the events of the previous year. While the manga is largely non-canon, especially after the Anzio OVA, it's interesting material for fans, especially fanfic writers.
As an adaptation of Girls und Panzer, the manga has its flaws, but it's worth checking out if you're a fan of Girls und Panzer.