Definitely IIT Roorkee.
ECE is a new course started at the Pilani campus. Even though the Pilani campus has the long standing history, IIT Roorkee is a better option.
You get access to the same set of oppurtunities in terms of placements, along with the old IIT tag at a lesser fees.
Also, in terms of research opportunities, IIT Roorkee is far ahead of BITS Pilani. Look at the Professors and their profiles at IIT Roorkee and BITS Pilani for yourself.
Thumb rule is, if you get an old IIT and BITS Pilani and if the course is the same, nobody leaves the old IIT for BITS Pilani.