FormatFactory. It's free, simple, and never disappointing me.. make sure to set AviSynth on, then you good to go.
update: only on the AviSynth if needed. I don't how it's work, some files when AviSynth is 'on', it's getting worst, but sometimes when the files you converted got problem like- the files runtime is not full/ loss some of it, then turn on the AviSynth can solve it. Most case, not needed.
