Which is better among IIIT Lucknow for CSE, NIT Allahabad and HBTI Kanpur for chemical engineering?

Go for the one which is nearer. Although, IIIT Lucknow is a fair enough option to consider for chemical engineering. All the above-mentioned colleges are national-level recognized colleges.

• The reason why IIIT Lucknow is slightly preferred over the others is because of its campus which is ever-growing and developing. 
• The recruiters are always eyeing the campus and offering packages as high as 10 LPA, which makes it quite a welcome option for all the applicants and aspiring candidates.
• Moreover, the campus will help you to focus on extra-curricular and other curricular activities too apart from academics, thus paying a lot of attention to the overall growth of the personality holistically and not just scoring good grades. 
• The multiple competitions and championships happening are always intended to prepare the students holistically.

You can go for HBTI Kanpur only when you have no other options of IITs or NITs. It is a state-level college and not as reputable as the others.