Should we prefer the new IIT over IIIT Allahabad and NIT Bhopal? 

If placements are your main priorities then your order of selection should be: IIIT Allahabad > NIT Bhopal > New IITs.

My reasons to support the above statements are as follows.

• New IITs are established recently and hence they would lack good faculty and facilities.
• IIIT Allahabad has a great placement record as it has an average placement of 12 LPA and won't be surprised if it increases, even more, this year. Strictly from the placement point of view, you should prefer IIIT Allahabad first, followed by NIT Bhopal and then the new IITs. 

Finally, I am not against new IITs, and it is true that new IITs will flourish greatly in the coming years, but you should choose a well-established institute over the new one.