Both the colleges are best at thier own place. But IIT Dhanbad has been established in 1926 and more number of batches has been passed out till date, if you will see in that aspect IIT Dhanbad has more number of students intake and faculty members than IIT Ropar. Both has better in-campus facility. Further CS is a good branch that too you are getting in IIT Dhanbad, so I think you should go for Dhanbad.

Neverthless you can compare these two colleges using this link for your own reference: https://www.careers360.com/compare-colleges

Hope this information may help you, All the best.