Which should I prefer, SVNIT mechanical or IIIT Vadodara computer science?

If you are not looking at the branch, then you should think about going to SVNIT for Mechanical. Having friends study in both the institutes, I might be able to provide some details about them.

However, if you have decided that you would like to go for computers and if you could handle that field, IIIT Vadodara is a pretty good choice.

But many people will also advise you to not compare the two branches as they are quite different. NIT Surat is a better option facility wise but let me tell you that getting a job in the mechanical core is quite difficult. A lot of students will also opt for software fields.

Placement-wise, IIIT Vadodara is the best as you can get a lot more than what you might be looking for in Mechanical. Hope this helps.