I should say that your choice in planning career is very brilliant but for the best results, think of all the Subjects (not the location) .... Which one suits you, your skills, your passion and can give a favorable turn to your career and your life.! 
But still, to give the answer :-

Either Civil Engineering @ IIT Bombay... or Mech. Engg @ Kharagpur will be quite good !  

CS BHU ... :)

B.Tech CS BHU  >  Guwahati B.Tech CS> IDD CS BHU > EC/Electrical Roorkee  > #2 > #1

Why? Civil has job issues in every IITs even in bombay and delhi. Why go for that unless your dream is civil. M.Tech in Mech and Electrical can get tough and it may take 6 years. Placement is also not better than CS( #4 option).

Roorkee doesn''t have MTech CS anymore. BHU B.Tech CS is best option from above. BHU is ranked higher than Guwahati in all reputed rankings. I suggested IDD CS for BHU as third option even though that is best in terms of placement due to CS companies prefering integrated masters due to extra specialization. But you get very good placement in B.Tech CS at BHU and Guwahati as well so that''s a non issue.

This year rankings will shuffle a bit due to IIT convesion of BHU. If you miss CS then you will get EC or Electrical at Roorkee based on your rank.