The software I had before was incredibly slow although that might have been my old mac. Can anyone recommend anything?
FLV Crunch and Xilisoft converter seem popular.

Do You mean dvd - mp4? if so handbrake is probably easiest.

Also sometimes use ffmpegx if the need arises.

Didge.

I actually got the MP4 bit sorted and not want to burn them to DVD so need avi-ts converter and they all seem to cost $30.

Not got 30p at the moment lol

If I understand you correctly and you have MPEG 4 files that you want to convert to MPEG 2 and burn to a video DVD , then ffmpegx can also be used for that purpose. Two of the convcersion output templates are for DVDs. Although ffmpegx costs $15 to register, it can be used as many times as you like before registration so you could use it now and then register when you have the $15.

No I have AVI files I want to burn to DVD

Does this DVD need to playable on a regular DVD deck?
If so, then something like Toast will do it. You need to building VOB files and all that malarky.
Unless, of course, your DVD deck is a clever modern job that knows about .divx and .mp4 and all that, in which case just burn them as a data disc and relax.

I use DivX Doctor II to convert them to an MPEG 2 for burning to disc.

Ok. In that case ffmpegX can do the conversion into a VIDEO TS folder and then Burn can be used to make the DVD.