Which isolated DC - DC converter solution is better
Without knowing more about your requirements we can't give a precise answer. It depends on your signal to noise ratio coming in, filtering, ADC converter, # of bits, post conversion filtering, ADC PSRR, what else is powered by that supply line, just how good to you need it. etc?
For example you might not care at all about noise near the switching frequency of the converter. The noise rejection of the ADC might be plenty. Or, you might care a whole lot because you're trying to detect a very low level signal with high precision in a way in your system such that switching noise is killing you.
You may not care at all about load transient response of the regulator because it never sees much. Or, you might be hitting it with a big current slug and then you have to take an ADC reading during the recovery and it's impacting your results.
The Murata part doesn't seem to have much for data. They're a tier 1 company who knows power so I'd bet they make a good part, but only data will tell.
The SN part looks generally solid as well.
My suggestion is to buy the Murata module and focusing on the signal chain. You'll learn at some point if you have power supply requirements and will have to address them at that point. Rolling your own with the SN part is fine but seems like extra effort without yet knowing whether it's beneficial.
You may not need a linear reg to filter noise at all. But I'd leave room for one in case you do.