I've never seen PGSM, but if I had to make a choice between the anime and manga . . . I couldn't.
The manga is definitely much better plot-wise. There is no filler. Everything is story, story, story. This is good! I'm a fan of science fiction and adventure novels, which are also very plotty.
But I'm also a fan of character stories. The manga is a character story, but only for one character -- Usagi. Takeuchi sometimes seems to forget that she has a cast of twenty-odd (not just the soldiers) to take care of. Sure, the other soldiers get their days, but not the way they do in the anime. And the manga villains (especially in SuperS, minus Nehellenia) just aren't as developed.
Also, I think the art in the manga is absolutely horrible. Takeuchi has no concept of anatomy and her art just looks messy. For the manga revival, her art was much better, but it was mostly just because the lines were smooth! I saw a picture of Princess Serenity in her notes with the same smooth lines, and I was like, "ooh, shades of what's to come!" If she had just done smoother lines, her art really could have looked that much better. But as it was, it just wasn't that great.
The filler in the anime bothered me a lot. But I did like that in the anime, you learn more about the supporting characters. Even if, when it comes to the soldiers, most of the attention is on Ami and Hotaru, everyone's personality is a little bit more filled out in the anime, and we have more attention given to them.
I think the anime and manga kind of each have their characters that they focus on and ignore. In the anime, Usagi remains really rather ditzy all the way through Stars, whereas in the manga she gets much more mature but never loses her spark. We learn more about Rei's past in the manga, as well as some of the motivations towards her proud, snobby exterior. Yes, she's sophisticated, but she's also overly dignified -- because she's afraid of what people will do to her once they get too close, and afraid of what she can do to other people. In the anime, Rei is glossed over, while we learn more about Magnificent Wonderful Perfect Submissive Quiet Shy Intelligent Many-Talented Ami (can you tell I don't like her much?) and all the great things she can do, and all the reasons why she's wonderful and everyone should buy her merchandise. The characters carry the story, and the manga and anime both have their faults when it comes to those.
It sounds like I like the anime better, but what really brings back the balance is SuperS and ChibiUsa. Both of these are undeniably better in the manga. SuperS is a much more mature story, and in the manga, doesn't have a huge big gaping ragged black void of a HOLE in continuity! ChibiUsa is also less hyperactive, less bratty, and more like her mother.
So in short, in case you tl;dr'd this: The manga doesn't delve enough into the villains and supporting characters but is much plottier and more mature than the anime, whereas the anime has too much filler but has more developed supporting characters and villains (except, notably, Beryl and Nehellenia) and is a lot funnier.
Incidentally, I think both the anime and the manga could have done without the Starlights and Kakyuu. They were interesting, but they didn't add anything to the story. They weren't crucial to the plot at all, except their own subplot.
Well, I think that's my Ramble Quota for the day all used up.

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