three different sets of daily ISOs -- what's the difference?

[Rick Thomas]

There are three (seemingly) different sets of daily ISOs at
http://cdimage.debian.org/pub/cdimage-testing/daily/powerpc/20040710/

http://cdimage.debian.org/pub/cdimage-testing/sarge_d-
i/powerpc/20040710/

http://cdimage.debian.org/pub/cdimage-testing/sid_d-i/powerpc/20040710/

Can anybody explain what the difference is?  And which one should I 
use for testing?

Thanks!

Rick