Which is better for Engineering Phy- IIT Guwahati or IIT Roorkee?

When considering Engineering Physics, the choice of the institute is a secondary factor while your inclination towards Physics is the primary concern. The course is not for those who take it casually without genuine interest in it.

I think IIT Guwahati is a better institute for EP. Those who have a branch change of mind should take the batch strength into consideration as only 10% of the batch is allowed to opt out of EP.

Thus, unless you're certain of EP, I would recommend you go for BITS or top NITs. This will help you if you are looking for a core course.