What is better Btech at Bits Pilani or IPM at IIM Indore?

The best would be to go for a B.Tech from BITS Pilani and then an MBA degree from IIM/XLRI etc.

IPM at IIM Indore gives you an IGNOU graduate degree and then a diploma. Even though you will do the last two years together with the PGDM students selected via CAT, you won’t get the same status as them. It will take a couple of years to get acceptance. Additionally, the legality of the course is vaguely defined. 

Choosing one of these options also depends on your career orientation. If you want a job in the technical field then doing a B.Tech from BITS Pilani is better. Go for IPM from IIM Indore, only if you are certain you want to get into management job roles.