Well, after using Xilisoft DVD Ripper Ultimate 5 for a while now, I'm very impressed. It does a great job of converting DVD's for my daughter (she has an iTouch and PSP) and my wife (she has a Nano 3g). It also does great for divx conversions (.avi's).
The UI is simple, yet gives me access to all the options I care about (and many more I don't). The latest update (12/30/08) seems to have solved a few glitches in the UI, as well as allow even more control (like limiting the number of cores to use, and since I have a quad core this also may be useful).
Overall I highly recommend it. I used to use AutoGK, 3GP_Converter, WinFF and XviD4PSP, and though I will keep them around, I plan on using this one for all my needs now.