Hello

Not much difference. The B. Tech courses offered by IIST , the curriculum is similar to that of IIT.

if you are strong passionate about avionics, space, aerospace Engineering. and in future have any idea of pursing higher studies then go for IIST

But if you don't have any specific interest , any highly concise about placements then to be in safer side select IIT .

Hope this Helps

ALL THE BEST!