Take CAT again, only if you are sure you will be able to convert an old IIM. Otherwise, go for IIM Udaipur. For an MBA, you shouldn’t choose a college based solely on placements. Placement will only help with the first job but what you will learn during your MBA will help you excel throughout your career. In that sense, the new IIMs are gradually catching up with the old ones. The curriculum and teaching methodology followed by IIM Udaipur is similar to that of the old IIMs. Most of the faculty members of the institute are well-experienced.
Being part of a new IIM is a different kind of experience. You will get to build up the culture of that college. Also, after your first job, the benefit of old IIM gets neutralized by your job performance.
Congratulations on converting both IIM Rohtak and IIM Udaipur. But you should consider various parameters before getting to any conclusion regarding what you should do.
Past academics:
Work experience:
Destination post MBA:
All these 3 factors should be taken into account for making the decision. The new IIMs do not have good facilities since they are still in their initial stage. But the IIM tag sure carries a certain weight. If you think you can do well and get a job from the new IIM, go for it.