When you compare both these colleges for their faculty, in my view, they both have top notch faculty.
For example, IIIT Bhagalpur is also mentored by IIT Guwahati so most students are aware that the faculty and academic environment is good here. As the case with IIIT Lucknow is also similar – where it is being mentored by IIIT Allahabad which is known for its coding culture and is one of the top IIITs across the country, you will not have a reason to doubt the institute.
So, both colleges are equally good as they are being mentored by some of the best institutes in the country and have good faculty.