I'm not sure what is the fastest (I was under the impression nero was suposed to be fast and it seems to be the fastest of the all in one programs I have tried). I think tmpgenc was a little faster but it is designed to be used with other programs (it does the conversion only). If you are using nero thier should be a log that comes up on the screen giving the time that various parts of it started and stoped. Try to determine how long the actual burning took (an 8x burn should take about 8-10 minutes).
Keep something in mind though, thier are two ways to convert various media files to a dvd. The first are all in one programs that basically do the whole process for you from start to finish like nero. I have tried a few other like the film machine, DIKO, dvd movie factory (only works with mpeg I think) etc. Personally, based on what I have tried, I would stick with nero if it is working well. It's kind of like doing movie backups though. Thier is more than one software that does it right and diffrent people will have diffrent opinions on which they like best. Dvd santa is suposed to be good but I havent tried it yet. Their are some free ones out thier if you would like to try them.
The other way is to use several diffrent programs and go through each step of the conversion yourself. This is suposed to be a beter way of doing it and gives beter results (I think it might be faster too) but thier is a lot more to learn. Personally I have stuck with the all in one approach (since it's lots easier).
Either way, here are some diffrent softwares that do this kind of thing. These are the all in one programs.
As far as doing it the hard way, it is usally best to find a tutorial and use the diffrent software that it recomends. Here are some tutorials.
Just click on format conversion and select the one you want to do (such as avi to dvd or xvid to dvd). Then click search or list guides.
Also, here is the forum on cdfreaks that deals with this kind of stuff.
This thread looks like it has a little bit of usefull info.
Thier should be several other threads about it too.
Sorry I couldn't be of more help but I have tried to stick to the easiest way possible of doing it (which has seemed to be nero for me). I prefer the point and click approach to doing it the hard way. The above links should point out some other all in one programs you can try including free ones and at least point you in the right direction if you want to go further than that.
Fyi, one other point. some programs may be a little faster or slower but the truth of the matter is, transcoding takes a long time no matter how you do it or what software you use. The only way to really speed things up is to upgrade the speed of your computer (processor, memory etc). Transcoding is very dependant on the speed of your computer. My main rig has an athlon 2500 overclocked to a 3200 with 512mb of pc3200, fsb running 400mhz on a good quality abit motherboard (not the fastest computer out thier but defanatlly decent) and it still take me a long time to transcode. I have 3 diffrent dvd burners and it just takes a long time, even if you burn at 16x with 16x media. Its not the burning that takes so long, its the rest of it.