Hey,

IIIT Una will be  a better choice when compared to iiit sonepat as it is the most progressive iiit's right now.
Both iiit are one of the 20 new iiits which were sanctioned in 2013 to be established in India. But compareling all the parameters including placements, iiit una anytime. The placement and job opportunities in iiit una are good, large number of companies do come to the college but most of the companies have their package of around 7-10 lakhs while only few companies offer packages above it.
 The faculty here is good most of them are M.Tech graduates and few are Ph.D. holder but the few teachers are quite friendly here and understand the students and adjust accordingly. Some have an excellent teaching style.
Hope this helps.