First of all, don’t trust the official figures regarding rankings for colleges. They are misleading and are meant for advertisement purposes only. No good college needs to show itself at the top of the rankings.
Now comparing VIT and Anna University, Anna University is definitely better in the ranking than VIT. Its CEG branch is at another level and not on par with VIT at all. Some points that support this opinion are:
Student quality at Anna University is better than at VIT.
VIT is a private university therefore more expensive than AU
The curriculum is harder in AU than in VIT, but the assessments are direct and easy here.
Placement opportunities are better at AU because of the variety of companies that visit the campus in contrast to the mass IT recruits that happen in VIT.
All these points strongly favor my opinion. One thing to keep in mind here is that when I say Anna University is better I mean the main campuses (CEG, MIT, ACT) not the affiliated colleges.