Hi,
I'm a bit confused.
* in your headline you speak about "delta sigma ADC" but in the text only of "ADC". So is your concern about ADC in general or only "delta sigma ADC"?
* you speak about "simply use VFC". I don't think a VFC solution is more simple than an ADC solution. It is not cheaper either and by far not as linear as a delta sigma ADC.
* then you speak about "better". But "better" without additional information is useless in a technical discussion. Better can be combined with: low cost, linearity, noise, part count, low power, PCB area....and a lot of other..
So I'm a bit lost what answer you expect.
Klaus