There are several trains running between Lucknow to Agra like Varanasi Marudhar Express, Guwahati Dwarka Express, Kamakhya Gandhidham Express etc but I choose Ljn Agr Intrcit(12179). Train is very good. It has clean toilet. Anyone can easily get reservation of this train either by tatkal or by normal ticket booking system.
Travel experience was very good as this is a direct train from Lucknow to Agra and timings are very convenient. The only draw back of this train is, this train has only one AC chair car coach which is always full. The best part of this train is that it starts from Lucknow and ends in Agra so no need to worry about the destination.