Got through watching just about everything for the first time and here's my thoughts:
The 1998 version is the best of all. Great twists, great humor, great everything really. I couldn't for the life of me predict what was going to happen based on the story titles (and that's the way it should be). The shorts are about as good as the 1998 version itself. I relate to all 3 of the girls and it seems the single full episodes are the most entertaining for me. Criss-Cross Crisis was both really weird because of where the voices were coming from but also really funny, especially when The Professor was trying to fix things. There were a few stories that weren't as good like Paste Makes Waste but that happens in just about every cartoon. The movie was fantastic and I highly recommend starting with it if you're going to get into the series as it came first in terms of story.
The reboot, while not as entertaining, it's not that far below the original for me. I just can't really see much of a reason to hate it but apparently it bombed in the ratings. It has a lot of great faces throughout and much of the villains from the original show return. I feel Buttercup saying "Don't call me princess!" is a line the original would've said too. Manboy was kinda disturbing though but at least there were also new villains. The intro and outros are pretty catchy too. Love the little animation that plays during the outro.
Powerpuff Girls Z really doesn't compare. It may be more faithful to the original show but it falls pretty flat with me. The girls end up making up excuses to leave class instead of flat out telling the teacher they have to save the world. Even when trying to save the world, they don't seem to do much other than use whatever objects they've become associated with. (Blossom with a yoyo, Bubbles with a bubble wand and Buttercup with a hammer). There's no hand-to-hand combat like the original and in 5 episodes I watched, it was only Mojo Jojo they fought. The intro implies there are others but realistically, I can't be bothered to finish the series. It's just too bland.
The 2 specials were pretty decent. The art style was certainly different and took some getting used to but apart from that, they were pretty much the same characters from the 1998 version.