Ellie, easily. Lana's voice and lyrics are just so listless and boring. Her schtick wasn't all that interesting to begin with but with every passing song of hers that sounds the same as all the others, it just gets worse and worse.
I was surprised by how well her voice goes with dance beats like on the Summertime Sadness remix, though. The remix itself was incredibly by-the-numbers but I'd be interested if she pursued something in that direction.