Choose UCMS if you get selected in both cause academics are better in that and it's increasing it's quality in it. The location around UMCS is quite good and is the have mistaken beautiful campus among all the medical colleges. 

If you complete your mbbs from ucms you get 50% quota in 3 colleges of Delhi also. 

Ucms have sports and all other extra curriculam activities too, it's better to chose ucms .