If you want a reliable, enjoyable Android experience, you need top-of-the-line hardware. Anything less than the best is going to really struggle with many memory intensive functions. Android is not optimized for lesser specs.

The 520 does lack a front-facing camera, but if you can live without that, it does 90 percent of what the top WP8 phones can do, and it's pretty reliable, too. WP8 can run just fine on lower-specced hardware.