epub to mobi/azw3 conversion tools?

Hi everyone,

I have PW3 and currently use Calibre to convert from epub format to mobi/azw3. I found that calibre's output sometimes the fonts and spacing is not as in original epub. I also tried Epubor and impressed with its output, which is very clean and fonts / space is much better than calibre. However, the resulting file is usually double size compared to calibre.

Is there any of you have experience other alternative converter that can made better output than calibre with similar size instead of double?

Thank you.

isa