What should I choose between LHMC, UCMS, and RML?

The best college for you depends on your priorities and goals. First, you need to figure out what exactly you are expecting from your degree and college. My sister had similar options as yours and she was looking for a safe location and easy commute, offering decent social life and good societies. She analyzed the pros and cons of each of these colleges and even contacted the seniors of these colleges. Here is what she derived regarding each college

• LHMC: The institute is famous for its prime location, brand name, and its safe all-girls environment. Its infrastructure has been renovated recently and its DU tag is very helpful. However, the patient load is less compared to other teaching hospitals in Delhi and if you live close by, you won't be given a hostel room either.
• UCMS: Being a co-ed college, it offers better exposure, hostel facilities, infrastructure, and an amazing patient load. This college too is under the DU and has some amazing societies and fests. However, its primary drawback is its location which is often considered unsafe, especially for girls.
• RML: Thistoo is co-ed and has a good location. It is considered to be the best medical college in Delhi after AIIMS and VMMC. Its IPU quota and newly established infrastructure are what sets it apart from the other two colleges. However, being new, it may be lacking in terms of reputation, alumni, and quality of fests. 

The academics are almost similar in these 3 colleges, so consider other pros and cons and make a wise choice.