I’ve only read the VNs for Umineko so I can’t say much about it… but I have experienced the three mediums for Higurashi; having read all of the eight original VNS, collected the main two seasons of the anime (hey Siren please release the OVAs) and collected about half of the manga.
I’ll start with the anime: I honestly think it’s a fantastic adaption and I like it a lot. Other than a few weird frames I think DEEN did a pretty good job. In a few ways it doesn’t quite live up to the original VNs, but I think that’s simply a limit of the medium, and it does an excellent job of animating some difficult-to-picture scenes. Like @kyuketsukimiyu mentioned above, some of the finer points of the mystery are lost, and as a result the second season has a few explanatory scenes that sort of fill the viewer in on stuff that hadn’t been included in season 1. If you’ve already read Higurashi in some form, the anime is a very enjoyable retelling of events with less attention to detail. I don’t recommend it as an entry point to the series, simply because I feel the mystery is better told through the other mediums.
The visual novels are my personal favourites. I read the original translations and am slowly making my way through the new Steam releases, and I might be biased since it was my entry point to the series, but I think they tell the story much better. It offers an insight into the thoughts of each arcs’ protagonist that can’t quite be recreated in the other media forms, which really helps the reader immerse themselves in the fear, paranoia and mystery of the early arcs. As more information is revealed, the protagonists seem to have their own theories about the mystery, but almost every arc has a huge twist at the end that turns the current theory on its head. Even the “club activity” sections, where the story takes on a slice-of-life mood were exciting and over-the-top, usually written from the viewpoint of a befuddled Keiichi as he attempts to trick the other club members. There are plenty of recurring phrases and motifs, and the Umineko VNs reference Higurashi’s an awful lot, be it with specific characters, remixed music or just things that Battler yells.
A great example of the VNs is a scene that didn’t make it into Higurashi’s anime, but is one of my favourites: Tatarigoroshi’s “1500 seconds” (on youtube here and here in two parts). It showcases the dissonance between happy and sad scenes that the VNs use so often, and you can really feel the protagonist slipping deeper into the madness of Hinamizawa. These visual novels are what I’d recommend to someone looking to get into the When They Cry series.
As for the manga, I’d say it’s another great adaption. I feel like the story translates better to manga than anime, especially the mystery elements, and the manga-only arcs such as Onisarashi-hen feel like another regular higurashi arc; full of suspense and mystery. Plus, the art is fantastic. I’m not finished reading through them all yet, but I would recommend them as an starting point before the anime, and any fan should read them.
I think it’ll be interesting to see how the upcoming live-action series handles the story, but I can’t say I’m expecting much after the live-action films…