What does the phrase "说不好比起~" mean?
'说不好' is a variant of '说不定' (can't state with certainty= may be)

'比起' means 'compare to'

'也' in this context means 'even'


&quot;说不好比起 C 也&quot; = &quot;May be even(?) compare to C&quot;
It is an incomplete sentence, we don't know what quality is being compared between B and C
The following would be a complete sentence:

&quot;[说不好]比起 C 也好不了多少&quot; - &quot;[May] not even [be] any better  compare to C&quot;
好不了多少= not even any better