1) Define "better"
2) An instrumentation amp IS a type of differential amp, with a high input impedance.
3) CM noise rejection: Look at the data sheets.
As noted, a comparison of the data sheets' common-mode rejection will give you the answer.
Note, that an InAmp may have a fixed gain different from what you need.
Any old instrumentation amp may not be what you need,
some ADCs want really stiff drivers to tamp down kickback
noise and such. More a high speed thing as I make it out,
but I'd take ADC mfrs' hints about well mated front ends.
DC CM vs HF CM is another point to ponder. Fewer options
if you're really after high frequency (conducted susceptibility
testing or whatever).