To my knowledge S3's original compressor is still the highest quality overall when taken generally over all images. This was originally available on S3's website, but whether it is still easily downloadable from anywhere now I am not sure.
Microsoft's compressor supplied with DX is not great.
I certainly wouldn't rely on a compressor from a company that doesn't even implement the spec well
(Sorry - cheap shot, but I couldn't resist. Actually I understand that the quality of nVidia's Photoshop compressor is actually much improved these days, although probably still significantly inferior to the S3 one.)
[edit]
Found what appears to be the original S3 utility at this link -