Inspired by a recent thread in the DVDFab forums, I thought I might list a few conversion programs that I've used with some success, and maybe a few that have caused some problems.
Lets start with the old standby conversions of dvd to xvid or divx avi files. This format is quickly losing popularity as most portable devices are being developed to playback mp4 or mkv files using H264, but there are still quite a number of stand alone dvd players that use this format.
One of the most commonly used programs for this was AutoGK. This is the user friendly version of a fairly complex program called Gordian Knot. It is basically set up so that you don't have to fuss with detailed settings, though those settings can be accessed if you need them. There are plenty of guides for using the program, since this has been around for at least seven years.
I've used it a few times testing, and never had issues. I believe it is limited to square pixel output however.
Other programs that can handle this type of conversion include Virtualdub, AviDemux, Xvid4PSP, WinFF, FairUseWizard, etc. I was never a fan of Virtualdub, but I seem to be in the minority with that.
Though I rarely converted to avi, the tool I used the most was FairUseWizard (the free version). I then moved on to AviDemux. I have no complaints with either for conversion to xvid avi. AviDemux has quite a few more capabilities, but isn't the most intuitive program. Take some time to learn its commands though, and it works quite well for converting, merging and cutting avi files. It also has tools for adjusting audio/video synchronization. I don't advise using it to cut mpeg2 files however, as it always seems to lead to issues in sync.
Moving on to tools that convert to dvd-video format, I have been a fan of AVStoDVD for several years now. Using the HC encoder, it can produce superb results...but of course, that always depends on the quality of your source. It can convert from too many formats to list, but it is quite versatile in its input capability. Its main weakness that I've found is conversion from blu ray sources that use DTS HD MA audio. Sometimes it works for that type of audio, sometimes not. If you are converting blu ray to dvd I suggest using BD Rebuilder in Alternate Movie Output mode instead. It also uses HCenc, and I've had a lot more success working with the problematic DTS audio sources with BD Rebuilder.
One program I most definitely do NOT recommend for conversion from blu ray to dvd is the section of DVDFab that is supposed to do this. I tested this some time back now, just after they released an "improved" version, and the results were just terrible.
Now we come to the more modern formats...mp4 and mkv. Handbrake seems to be the most commonly used program for this, though there are many who also like Xvid4PSP and Ripbot264. If you are masochistic and a detail freak, you might want to look at MeGUI, but as you may have noticed, it is not my favorite program.
BD Rebuilder can also do conversions to these formats, but only if you start with blu ray sources. Handbrake and Ripbot264 are more versatile. If you need specific output sizes, well, Handbrake has recently done away with the option to use a 2 pass encode with size as the main constraint, so you'll either need to use an older version of Handbrake or use a different program.
Handbrake is set up to make your life easy....the developers tend to be a bit headstrong, but they have worked hard to make the program's UI polished and accessible for virtually any level of user. There is another program that is based on Handbrake that I also recommend looking at. It is called VidCoder.
All of the programs listed here are free to use (with the paid version of FairUseWizard and DVDFab as the only exceptions). So it should be obvious that good quality conversions are available for NO cost, and the ease of use can match virtually any commercial program you want to compare them to.
If you have some favorites to list, please do so. Or if you've had trouble with some programs, that information could be helpful too.