The second age features locomotives that are nice in all aspects. Csd 321 (1) and Class 65 (2) are trains available immediately after you reach this age. GS-2 (3) can be bought only if you upgrade the depot.
Csd 321 is an interesting choice. Although its price and upkeep are high, it features a nice speed/power ratio. And it only requires green tokens.
Class 65 is the best locomotive in this age. It has decent statistics and it doesn't cost much. However, you must pay for it in yellow tokens and the fuel costs black tokens. It is recommended to switch most locomotives for this one. It is the most useful train in this era.
GS-2 is a powerful locomotive that not only has great weight, but a powerful engine as well. Price, upkeep and length are its disadvantage. It takes much place that could be used to add another carriage. It is best to use this locomotive for heavy transports or connections that you want to be very quick.