These are good universities. Now please understand that the syllabus for all of them is the class 12th one. So prepare for them using that. COMEDK has a mock test that will be announced soon. SRM has a sample paper, check that. The exams are not very tough if you prepare. 

I didnot understand what you meant by how to select in these exams? What do you want to select? Or are you asking which is the better one? Please clarify and I shall get back to you.