AVCHD was chosen as the highest-quality format for the 1.0 versions. It was chosen because it could fit on a DVD9 and then be played back on many Blu-ray players.

With 2.0, the DVD9 size limitation was abandoned, allowing for less compression. Currently the highest-quality format in the 2.x series is MKV, but there will also be a Blu-ray ISO in the future. AFAIK they will have the same video quality, although the Blu-ray may have better audio options.

It sounds like you've found the best versions of all of the films, as they stand right now.