I disagree here. Umineko and Higurashi, although both extremely long, are in their own separate continuities and Umineko has no connection to the plot of Higurashi. To be purposefully vague there are some character references between the two series, but it's not assumed that you've read Higurashi. It's kind of like reading the original Doyle Holmes stories before watching any of the numerous adaptations - it's interesting to see reinterpretations, but everything's written under the assumption that you are unfamiliar with the original work.
But the major problem is that Higurashi's translation is simply bad. The first 4 books are terribly edited (although this can be fixed by a fan-edit, if you can find it...), the next 3 much better, and the last book is terrible again. Despite being a fan-translation, Umineko is much more painless to read through - I suggest you start with Umineko. If you enjoy it, then go back to Higurashi and you'll be able to keep reminding yourself that underneath the poor English is a great murder mystery. If you start with Higurashi I fear it may just put you off the whole series.