The only important thing (for me) that A-300 has and the new Dune doesn't have is the Bluray Menu support. So if the Bluray Menu is not important, go with Dune for sure. You also have more control with Dune's interface with background images and covers and all that.
If you need Bluray menu support, avoid Dune and go with A-300.
You must know that for the moment, A-300 can not play live mms streams.
A-300 supports 3d MKV in which if you put the right flag in your...