Does BIET Jhansi and KNIT Sultanpur Computer Science better than non-core branches at IET Lucknow?

As you have come up with this doubt, I assume that you have got a good rank in UPSEE. So, congratulations on securing a good rank in UPSEE that gave you the opportunity to choose from such elite institutions.

Unless and until it is an IIT, core branches are always a better choice than non-core branches.

Forget about non-core branches in UP government colleges, there is not much facilities and exposure. So, if you are getting a chance, it is highly recommended to go for CSE in BIET or KNIT because in CSE or IT, you just need a laptop and good internet connectivity and these colleges provide WIFI facility. You will have to indulge yourself in regular practice to bring the best out of yourself, as everything is available on the internet.

CSE would be a better choice if you look forward to getting placed after your graduation. If you want to pursue higher studies then, non-core branches at IET Lucknow will give you a better exposure such as coaching institutes, because of its location.