Help required in DVD ripping

I use DVD Decrypter rip dvd and AutoGK to convert it to Xvid 700 mb but i dont get the same quality of the original Dvd after converting to avi.file ?

My question is here which software is best to rip a dvd and then convert the same file to xvid uptill 700 to 750 mb with better picture quality and sound.

Kindly guide me out with tutorials.

thanks.