The worst epubs are bad because some jackass took some poorly OCRed text and dumped it into the format. The best (retail) epubs are on par with the best PDFs except you don't have to pan-and-scan to read a fucking page. It just reflows.

For novels I want and prefer epubs, but also non-novels if they were released in the last 5 years or so. PDF isn't magic, and there are bad pdfs out there too, scans of photo-copied books and other nonsense.