NIT Puducherry is very new compared to College of Engineering Guindy (CEG). Let me share some points which might help you decide.

• CEG is very old and experienced as an educational institution. It has well-established CSE and ECE departments with exceptional and updated lab facilities.
• The syllabus is more or less similar in both colleges.
• CEG has a more competitive student crowd which eventually helps students to boost their morale. 
• Due to its years of educational experience, CEG definitely has a better placement record than NIT Puducherry.

It is recommended that you go for CEG if you have to choose between these two. But if your choice only is NIT Puducherry then you can opt for it. It is a good college but as it started functioning recently, it is better to go for an experienced one.