If IRCTC train ticket booking is your primary requirement then go with IRCTC Co-Branded CCs like:
IRCTC SBI Platinum Card
IRCTC HDFC Bank Credit Card
Or else make an estimate list of all your yearly spending(both online & offline where a CC can be utilized) and choose CCs that will benefit you the most of your overall spendings.
You can use DCB or Infinia cards as well from HDFC. They provide around 10% back in points. 3.3%*3x if you use smartbuy to buy the ticket. There is no issues with buying IRCTC tickets from smartbuy.
Some credit cards like IDFC First Bank Credit Cards: Millennia/Classic/Select/Wealth , AU Xcite, Xcite Ace and Xcite Ultra, Altura/Altura + Credit Cards offer Free Railway Lounge Access which is pretty good in the cities it is available.