Tsukhime, probably. I can't really remember E17's length, but its longer than Tsukihime. Umineko has freakin' 8 parts which are somewhat lengthy individually; I've never finished one in a day. You can finish one arc in Tsukihime each day if you try.
It's also the oldest, so you might lol at the art style at first, but its one of the greats.
(also gsen >>> all of them put together imho)
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'But what a passionate guy! He must be Italian or something!'
KrahenProphet and Kana are on opposite ends of the Awesome Spectrum.