Whats the best program for Compressing to MP4 format?

[Bansaw]

I have an AVI file and I want to compress it to MP4 format (progressive).

I have used Sony Vegas, the 6Mb maximum setting and it does an OK job but would like to explore other programs.
Can anyone recommend any software that would do the best job?

(I have Adobe Premiere Cs3 in case you can think of a plug in)
One of the delivery options is a "video frame" that takes an SD card for example...

[Baldrick]

MP4 is just a container but I guess you want mp4 with h264 video.

I would try a x264 encoder frontend like handbrake, vidcoder, tx264.

[MilesAhead]

Also coming along is TEncoder. It was just updated to 3.0. It has a choice of MenCoder or FFMpeg video encoders. It's multi-threaded and optimized for batch. Very handy also for muxing to another container while only encoding audio. The default is one pass mode. But it has an option to enable 2 pass. Currently it can only hard sub the video using MenCoder. But I believe the author is working on .avs script input to enable FFMPeg to perform more tasks.