Can anyone suggest best University for MS in Aerospace Engineering in USA and UK. Also amomg these two which country has more job opportunities for International Students.?

According to my research, I would not recommend MS in the UK. Yes, there is now a two-year stay-back period in the UK that allows you to look for work after graduating. However, the number of jobs available in the UK in a variety of sectors is extremely limited. MBAs and finance graduates with prior work experience are typically doing well. As a result, the course you choose becomes extremely important. Because of the abundance of available jobs, the United States, Canada, the Netherlands, and Germany are far superior destinations for technical courses. The United States is a far better option because there are far more job opportunities. STEM courses also provide a three-year OPT, making it a safe investment. As a result, the ROI is far greater, and there is also the possibility of career advancement. Even though the cost of education is higher, you get your money back and more. Here is a list of universities that you can target in the US:

Massachusetts Institute of Technology
California Institute of Technology 
Stanford University 
Georgia Institute of Technology 
Purdue University 
University of Michigan 
Here is the list of some of the prominent universities in the UK:

Cranfield University
University of Leeds
University of Manchester
University of Glasgow
University of Nottingham
University of Southampton
University of Surrey
King's College London
University of Liverpool
University of Sheffield
If you have any further questions just ask me.