from my totally amateur noob perspective... intellijel's shapeshifter is the craziest, most unique, overflowing with tonal possibilities (even including multiple forms of vocoding!) if REALLY hard to understand, and not analogue, module. that & as mentioned, the equally crazy as far as filters go, morpheus can do tons of stuff traditional analogue can't.
for me... TONE is the absolute highest priority & you couldn't pay to corrupt my rack with too hard to wrap my head around maths (i'd rather break all of its functions down to individual modules myself) or a sequencer & make self modulating patches.
shapeshifter is virtually a synthesizer unto itself it's soooo deep. that... and it would eat up so much rack space you wouldn't be able to fit ugly ugly ugly maths in it. HAHAHAHA!