I also use Zenni; best deal out there for prescription eye glasses. If you buy any designer frames, you're getting ripped off, period, end of story. The Frames from Zenni are just as good as designer brands and way better than brick and mortar discount places in my experience.
The only problem with Zenni is, if you have problems with the glasses like you need to fit the frames to your face or adjust them, you're on your own, but it's easy once you learn.
I'd go with medium index plastic lenses with anti scratch coating, it works good. Polycarb lenses don't look as sharp with a high prescription IMO. I tried their very high index lenses and got some distortions, but my prescription is crazy, I'm darn near blind!