Dear Jayanth

If you choose B-Tech Course, you will get bachelor's degree in Technology after 4 years. If you choose Dual Degree course, you will get both Bachelor's degree in technology after 4 years and Master's degree in five years. Normally if you do your M-Tech after B-Tech , you will require two years. But if you choose Dual degree, you get both B-Tech and M-Tech degree within 5 years So, you save one year if you opt for dual instead of normal master's degree after graduation.

So Both , B-Tech and Dual are fine in IITs. It depends on your choice , whether you want to do post-graduation course or not.........

All the best 

Hope this helps