I went back and forth between Moon Reader and Aldiko. I'd say Moon Readeris better, but both seem to rape the battery.
I recommend that you turn the option to execute a certain function on shaking the device, this may be the cause for consuming too much battery as it forces the accelerometer to remain active while reading all the time.
The best reader is this one with awesome user interface and page turn animation
Onle bad thing is that it doesnt support English yet https://play.google....WRlckZyZWUiXQ..
You can convert your books to AZW3 format and use the Amazon Kindle app. It works great and has one of the best reading experiences.
For converting your books try the site posted earlier: ebookconverter.net or use Calibre, which is a book manager/library. It can convert and transfer your books to the Nexus 7.