Sadly, they're all pretty weak. Software Sculptors, ADV and funimation have all licensed parts of the shows over the years and all have screwed up the translations. ADV having the worst of the bunch, completely changing spell names, the Dragon Slave chant and the usual ADV dub alterations forced into the sub text.
Its just a prime example of how 'official' subs are usually even worse than fansubs.
>Not watching Slayers in the superior german dub.