Hii,While the comparison wouldn't really do justice to either college, it is human nature to compare so I guess I'll try and make the compare. I did my MBBS from JIPMER and it was awesome. However I do believe AIIMS is better than JIPMER. I'll try and highlight the differences as I see them

Jipmer enrolls more students every year than AIIMS so the student teacher ratio is higher in JIPMER. This carries forward to a higher student patient ratio when one patient is examined for a class, though it doesn't ordinarily affect learning,AIIMS has a larger hospital, more patients, better equipment and hence your learning experience will be more thorough provided you take the interest to learn. From what I have heard, AIIMS teachers leave a lot of learning up to the students and if you don't want to learn you won't learn, but if you want to learn you can learn a lot. But in JIPMER the teachers teach a lot of theory and practice and even if you don't want to learn you end up learning. I know this is true for JIPMER, not sure if it's true for AIIMS.The variety and types of cases you would see are probably similar since both serve as the major referral hospital in their region and receive all types of cases. Although AIIMS refers a lot of standard and simple cases to other hospitals so you will probably not see too many such cases while in JIPMER, you see all types of cases.AIIMS has better research facilities and funding so if you do plan to do research projects you probably will be better equipped in AIIMS.

Internship in JIPMER is thorough, you don't have light postings and you learn a lot in internship. You also get a lot of hands on experience and clinical practice. From what I know in AIIMS, other than 4 or 5 months the rest of internship is not very thorough and the clinical training isn't as good.Both colleges have strong alumni networks that and reservations for post graduation courses that help you get into good courses and jobs after finishing your studiesDelhi being a metropolitan city has better recreational activities. However if you're a fan of beaches, and calm and clean weather, Pondicherry is a win.Pulse is the largest intercollegiate medical festival in the country and spandan is probably the second largest. Pulse definitely has better cultural activities while spandan definitely has better sporting ones.As far as post graduation and superspecialty courses go, AIIMS is usually better barring one or two fields.Like others have stated, if you get into either of these colleges you'll be in a pretty good position. But if you have a choice between AIIMS and JIPMER, then you should pick AIIMS.