[Ken Maltby]

Hmm... This could take awhile.

As to which I prefer, at this time I would say Koreader, for what I read the most. But, both are developing rapidly, and both are fully functional now.

There is no cost/disadvantage to adding both to an AuraHD 281. There is no change to the way your existing Kobo software (Nickel) runs, in fact the two programs appear to Nickel as just another book or image. (I personally have no need for many of the "features" in the Kobo software and find the way it processes files to be annoying and troublesome. So I keep my thousands of ebooks in folders inside a hidden folder, which keeps them away from Nickel's processing. But, you need not do this to enjoy the two alternative readers.)

The alternative ereading programs are primarily for, well .. reading. For reading from a much larger number of file types than the Kobo software. (For me the inclusion of .pdb files is significant, others might have their own.) There are a few posters who find Koreader's PDF rendering much better than what the Kobo software provides.

The main functional improvement, from my point of view, is that both use a file browser to select your books, and that you can use a folder/subfolder and filename system of your own, to manage your library.

As for all the capabilities of each, and how the same features are implemented, for each of the programs, that would be a large post and would have to include notice that the development continues with features added and improved all the time. (Koreader has nightly builds that are actually more like beta software and the port of Coolreader gets updated within a few days of an issue being raised here.)

Why not just install both and see for yourself? Both work fine on the AuraHD 281. If you find that you could use some tips, like where to poke the screen to bring up the menus or something, the users here will gladly help out.

Luck;
Ken