I can give you some information on both institutes since I have friends from both IET Lucknow and JSS Noida. Based on the reviews that I got from my friends I will say choosing JSS Noida will be better. It has a locational advantage, which plays a crucial role.

• The curriculum of JSS Noida is in accordance with the current industry trends. In the first two semesters, you will learn the same courses as any other engineering institutes in India. You can get the detailed syllabus from the website.
• JSS has a good reputation in the industry. Alumni of the institute are working on Google, Microsoft, etc. Many reputed companies visit the campus for the placement drive including IBM, Wipro, TCS, Amazon, etc.

For IET, the location is an issue. The faculty and curriculum are not that great either. So, I will suggest you choose JSS Noida.