IIT Mandi is a much better option than others. They offer effective classes along with commendable campus life and atmosphere. If you are intensely interested in the Electrical branch, then you can surely opt for it.
Otherwise, IIT Mandi has the advantage of a branch change policy that allows you to switch your branch to CSE after the completion of your first year in Electrical. This impressive policy made IIT Mandi stand out from other institutes.
IIT Ropar is also good enough for you, as they offer power-packed classes conducted by experienced and renowned scholars. Out of the three institutes, IIT Mandi would be an elite pick.