There are different review websites that compare different versions of DVDs.
DVD Beaver (they also host another website's comparions
And if you use
DVD Basen, a DVD review database, you should be able to find reviews and/or comparisons of DVDs you are interested in. You'll find that other countries like Japan sometimes get better transfers/audio (Superbit, non-SB, releases we don't get here).
I personally have SB versions of:
Spider-Man 1
Spider-Man 2
Fifth Element (got it right before Ultimate Edition, with the same Superbit transfer, was announced)
As stated above, the DTS track on SB versions is also a welcome addition (even though sometimes the difference is minimal).