What should I choose between UCMS, Delhi and KGMU, Lucknow?

Without any second thoughts, go for UCMS. The academic ambiance is almost the same at both the colleges and both of them are highly reputed. Here are a few additional benefits of choosing UCMS over KGMU

1. You will not have to go through the rural bond
2. Generally, colleges in Delhi are far better than the colleges in UP. So as 50% of seats in NEET are reserved for State counseling admission to UCMS will be far easier.
3. Under the UP system, extra merit is given to those who have worked in PHCs for state counseling making it difficult for a fresher. Delhi doesn’t have such a policy.
4. Life outside campus is fun both in Delhi and Lucknow. Lucknow is known to have excellent food places while Delhi is the capital city. 
5. UCMS allows its students to attend the festival of various other Delhi colleges including AIIMS's Pulse.

Overall, both colleges have their strengths and weaknesses so choose wisely!