What should I join, NIT Warangal or DTU/NSIT?

Since you didn’t mention your branch of preference, it is difficult to compare these institutes. The table below show a brief overview of the institutions. 

An overall comparison of these institutes is given below.

Administration: (DTU, NSIT> NIT Warangal)

• NIT Warangal is a reputed institute and you will be among good peers. However, the standard of teaching faculty, administration of the institute started lagging behind since 2012. The infrastructure is also not at the same level as it used to be. 
• The administration at DTU and NSIT is better than NIT Warangal. DTU and NSIT have maintained their reputation over the years.

Brand Value: (DTU~NSIT~NIT Warangal)

In terms of brand value, all these institutes are on the same level.

Placements: (DTU~NSIT~NIT Warangal))

• Most recruiting companies do not travel from north to south for tier 2 colleges like DTU, NSIT, NIT Warangal. 
• Placement opportunities offered at these institutes are on par. Salary packages offered to depend on the merit of the students.

Location: (DTU, NSIT> NIT Warangal)

• NIT Warangal enjoys a locational benefit for placement as it is situated close to Mumbai, Pune, Bangalore, and Hyderabad. However, Warangal does not have an airport which is a disadvantage.
• For startup/off-campus initiatives/NGOs etc DTU/NSIT offers better opportunities as these are situated in the country capital.

Social life in Delhi is definitely better than in Warangal. For all these reasons, choosing DTU or NSIT will be better.