Both the ECE and Mechanical courses are good, so you should choose the course you are interested in.
The first batch of Electronics and communication batch in IIT Bhubaneswar will pass out in 2020 which is why placement stats are not available. However, IIT Bhubaneswar had a good placement record in the academic year 2018-19, 90% of students got placed with an average of 11.4 LPA from IIT Bhubaneswar.
Out of 32 students, 29 students in the mechanical branch got placed in reputed companies with an attractive package in IIT Indore in 2018. The highest package was offered was HPCL that is 16 i.e. lakhs. The average package in IIT Indore was 9.13 LPA. The top recruiters who come for placement in IIT Indore for mechanical are ISRO, TATA MOTORS, HPCL, L&T.
The faculties at both the IITs are outstanding. Now, coming to course Electronics courses falls between in the middle of core and software. So, Electronics students get jobs quite easily in the software domain also. ECE students have a wider scope than the mechanical branch. If you compare college then IIT Indore will be the better option than IIT Bhubaneswar but if your interest is in the subject then ECE will be a better choice than mechanical.