If you are solo, the best vehicle option Guild wars platinum is the Demolisher. It has a long range siege attack as well as a battering ram, either of which can be spammed while the other is on cool down. It also moves relatively fast and thus can get to the fortress sooner. Unless you have a gunner, do not pick up a siege tank. Half of your vehicle will be useless, you will be moving too slowly, and you will be extremely susceptible to player assault.