Diploma

For sure an MBA has better and larger placement options.Major differences between MBA and PGDM are as follows :
MBA/MMS is offered by 'Universities' or 'Colleges that are affiliated to Universities' or Central Body directly under the Indian Govt while PGDM/PGP is offered by individual colleges and IIM's.
Fees is high in case of PGDM/PGP as compared to MMS/MBA.
PGDM is much more flexible in terms of syllabus as syllabus is not bounded by a particular university.
Ideally PGDM program is residential while MBA is not.
Examples of PGDM/PGP Institutes in India are- IIMs ,XLRI, SP Jain, NMIMS (Banglore/Hyderabad) etc.
Examples of MBA colleges in India are- IIFT , JBIMS , FMS ,NMIMS(Mumbai)SIBM (Pune), IITs etc.
Why few offer MBA and rest offer PGDM?
As per the law in India, only a University can offer degrees such as the MBA, BBA, B.Tech or B.E. Any educational institution which is not affiliated to a University cannot offer a degree. So institutes like IIMs, XLRI, NITIE, MDI etc. which are the autonomous bodies and run independently, cannot offer MBA degree and hence offer the PGDM / PGP.
PGDM / PGP
PGDM expands to Post Graduate Diploma in Management, while PGP is Post Graduate Program Diploma. And all the confusion starts when you see the term Diploma. Yes, you read it right this is Diploma and not exactly a degree in technical terms. The main reason why postgraduate courses are named as PGDM is because when an Institute is an autonomous body (not affiliated to any University) and conducts management courses, then such Institutes cannot offer MBA degree. Even IIMs, XLRIs doesnt offer MBA degrees; they only give PGP Diploma.
In purely an Indian context, there is NO DIFFERENCE when it comes to how the industry treats PGDM and MBA graduate. If you see, 9 out of top 10 B Schools in India offer PGDM / PGP and not MBA. This is the testimony to the fact that there is no difference between the two in India.
Career growth is same in both, and to be true career growth is dependent on individuals performance and not on the name PGDM or MBA. Starting packages are dependent on colleges name and brand, not whether it offers MBA or PGDM and that is why you see most of the top B Schools in India offer PGDM/PGP and only couple of colleges offering MBA degree compete with them.