we did the triangle couple of years back,i recommend you take a package from any tour operator, we took the package from RBS travels.
i feel road is better than the rail,
and if possible change the order of your visit,delhi > jaipur > agra, coz once you visit taj in agra nothing in jaipur will look good(jaipur is wonderful though)
taj is best at dusk and dawn.....
i can go on and on ...................