Which is better: civil engineering at IIT Bombay or electrical engineering at IIT Roorkee?

In my opinion, the institute is more crucial than the branch as academics rarely matter for an IITian. What actually matters is how the college molded him from a fresher to a mentally stable and talented person who has honed his talents to the fullest through maximum exploration.

That being said, I would recommend you to go for IIT Bombay irrespective of the branch you are able to make it into. 

• IIT Bombay has its own legacy of being an IIT from the start whereas IIT Roorkee was a State University initially. Hence it is still undergoing changes. This eventually limits the opportunities offered to the students especially related to research work. At IIT Bombay many universities and R&D labs approach students for internships. 
• The rules for girls and boys are equal at IIT Bombay, unlike IIT Roorkee which discriminates between the 2 genders. 
• Because of its location, IIT Bombay, the finance capital is preferred over Roorkee. 
• The placements are better at IIT Bombay Civil than at IIT Roorkee Electrical, so need not worry about jobs. 

Overall, IIT Bombay will give you a sense of freedom to explore everything and broaden your opportunities.