There are two good trains available that could be useful especially for tourists. One of them is Shatabdi Express and the other one is Taj Express. Shatabdi is much more comfortable than the Taj Express. Entire train (Shatabdi Express) is air-conditioned. Two type of seats are there in the train, air-conditioned chair car and 1st class executive. Photo of the both the classes available here below:

 

The second option before tourist is Taj Express. While this train is not as fast and as good as the Shatabdi one. But still air-conditioned chair car seats are quite fine.

Photo of the train is available here

 

More info.

Shatabdi Express – Delhi to Agra: A/c chair car – Rs. 455/each | A/c 1st class – Rs. 900/each

Timings – Depart: 0600hrs, Arrival Agra: 0755hrs

Station: New Delhi in Delhi, Agra Cantt in Agra

 

Taj Express РDelhi to Agra: A/c char car РRs. 300/each  | Ordinary class РRs. 120/each

Timings – Depart: 0700hrs, Arrival Agra: 1000hrs

Stations: Nizamuddin in Delhi, Agra Cantt. in Agra

 

Traveller could  online book tickets through Indian Railways or IRCTC website using net banking or credit card.

Website Address – http://www.indianrail.gov.in/ or https://www.irctc.co.in/

 

Above are the best trains but if two doesn’t solve your purpose, here are some more train to Agra from Delhi:

Hirakund Express – 0810/1145 Hours

Samta Express – 0840/1130 Hours

Mngla Express – 0920/1220 Hours

Goa Express – 1505/1745 Hours

AP Express – 1730/2037 Hours

G T Express – 1840/2145 Hours

Bhopal Express – 2100/2335 Hours