Are IIIT Allahabad and IIIT Delhi better than NIT K, W, T (comparing CS and IT)?

If you had specified the parameters on which you are judging the institute, it would have been easier to answer the question. In terms of quality of education, the two IIITs are better than the three NITs. 

Given below is a brief comparison of the institutes based on various parameters. You can make your decision based on that. 

Faculty:(IIIT Delhi > Top NITs ~ IIIT Allahabad)

IIIT Delhi has the best faculty. Even top NITs don’t come close to IIIT Delhi in terms of faculty. 

Campus Life: (Top 3 NITs > IIIT Allahabad > IIIT Delhi)

The top 3 NITs offer better campus life. As compared to NITs the workload of IIIT Delhi is too much. IIIT Delhi also does not have as many clubs and societies as top NITs. NIT campuses are also bigger in comparison. 

Hostels: (Winning Institute - IIIT Delhi)

• IIIT Delhi has better hostel facilities as compared to any other Govt. college or even some IITs for that matter. In summer you will get air conditioning and a heater in winter at IIIT Delhi. There are also sports facilities like Foosball and Swimming Pool, etc. 
• Other facilities available at IIIT Delhi are quite similar to that of NITs and IIIT Allahabad.

Placements: (IIIT Delhi ~ Top NITs ~ IIIT Allahabad)

In terms of placements, IIIT Delhi matches the placement statistics of top NITs. A student of IIIT Delhi has recently secured a placement package of 1.45 Crore. The average package of the institute mentioned in the question is around 15-17 lakhs (for CSE). 

Location: (IIIT Delhi > Top 3 NITs ~ IIIT Allahabad)

• IIIT Delhi enjoys the benefit of being situated in the capital. The city life, start-up culture, and many internship opportunities are some of the perks of attending IIIT Delhi. 
• Whereas, the top 3 NITs are situated in small cities. IIIT Allahabad is also located in Prayagraj, which does not offer a good city life or enough exposure. 

But whether you will like the campus or not depends on your background. If you are from South India, life in Delhi or Prayagraj may not be that appealing and vice versa. 

Reputation & Alumni Base: (Top 3 NITs > IIIT Delhi > IIIT Allahabad) 

• The top NITs have more recognition among the recruiting companies due to their legacy. IIIT Delhi is a fairly new establishment in comparison. Even though it is growing at a rapid pace, it is still up to the standard of the top NITs. 
• The alumni base of the top 3 NITs is also better due to the same reason. 

If you are genuinely interested in coding, you should choose IIIT Delhi or IIIT Allahabad. Otherwise don’t go for IIITs.