Since I have friends from both VIT and Thapar, I think I can answer this.
Thapar University:
VIT:
VIT Vellore is yet to be at par with Thapar University. Since VIT takes in a huge number of students, the placement quality is declining over the years. The average package at VIT is around 2-3 LPA.
Unless VIT Vellore is closest to your place do not opt for it. Thapar University is better in comparison to VIT Vellore. Hence, go for TU without any hesitation.