The US releases all have problems, different problems but problems nonetheless. :/ Disney is lame. I'd recommend the HK release for Laputa at least, as the US release has dubtitles.
The HK release of Laputa has no english dub option at all, and is missing many of the extras found on the US BD.
http://forum.blu-ray.com/showthread.php?t=198710
Here is an OK discussion of the pro & cons of each version, but it is not clear that the JP versions are universally better.
For example on Nausica,
Picture: The JP / US Bu-rays are indistinguishable in motion so I'd say that both are winners here. The HK version is also pretty good (minus some problems) but the subtitles are an annoyance.
Audio: If you're interested only for the JP audio, I'd suggest the JP release. If you want both versions in lossless, the US release is your friend.
Extras: The US release does not contain the excellent audio features. The Japanese release does not contain the 12-minute interview with Miyazaki and the Behind the Microphone feature but it contains the mini-book and AR (afureko) recording script. If you're not interested that much in the interview, script and mini-book, I suggest the UK release.
Or looking at the extras for Laputa,
JP
Storyboards via Picture-in-Picture
Theatrical trailers
AR (afureko) recording script
Credit-less (non-teroppu) opening and ending sequences
TV CMs
Promotional videos
US
Introduction By John Lasseter
Original Japanese Storyboards (2:04:41 in 1080p)
Behind The Studio: Explore The Movie's Fantastic World
- The World Of Laputa (2:19)
- Creating 'Castle In The Sky' (3:41)
- Character Sketches (2:40)
- Producer's Perspective: Meeting Miyazaki (3:14)
- Scoring Miyazaki (7:18)
- Original Japanese Trailers (4:07)
- Behind The Microphone (4:08)
The JP versions are a 100% markup to their US counterparts, and whether or not they are better is sometimes murky.