Should I Join Kj Somaiya College for Computer or take a drop and Aim for VJTI?

Between KJ Somaiya and VJTI, the latter is definitely better. Whether or not you should take a year drop that depends on you and how important is this year to you. 

Comparison:

If you compare KJ Somaiya and VJTI, in terms of placement and higher education you will see that the best students from KJ Somaiya do get similar opportunities as VJTI students. One of my friends attended VJTI and got placed in a company that was one of the best to visit KJ Somaiya too. So, he has 4-6 colleagues from KJ Somaiya. 

As long as brand value goes, after 5 years of the compilation of your course, no one will care where are you from VJTI or KJ Somaiya. 

People will care if you are from IIT though because IIT brand-name sticks. 

A word of advice, dropping a year to join VJTI may not be worth it. If you are going to drop a year, try to get into an IIT or IIIT.