If you want the look to be the same, MOBI ==> EPUB should work pretty well, and EPUB ==> MOBI will only support a part of what could be in the EPUB (for instance, no embedded fonts). AZW3 as stated will be pretty much equal to EPUB.
If you want the code to be the same (possibly for editing-related purposes?), do not use calibre to convert. The css will be flattened, into calibre** styles that display the same across all devices but are annoying to edit.
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