Though it was my third time to Agra and probably for the shortest duration, this was the most beautiful experience. My friend and I took Gatiman Express from H Nizamuddin around 08.10 am and reached Agra around 9.50 am. We just had 1 day as our return train was in the evening at 5.30 pm. We visited 4 to 5 monuments but regret not visiting Fatehpur Sikri.
Tip: Never go Agra in May. It's too hot and even we were aware of the fact, we wanted to visit.