What is the best video conversion software?

I’m trying to convert an mkv file to an avi. I want the best, most reliable software. I don’t care that if it costs money. I want the audio and video to sync. I want good quality audio and video. And I prefer not to have watermarks on the converted videos.

I’ve tried these following programs and they didn’t work out for me:

AviSynth
AlltoAvi
Total Video Converter
ImTOO