What do you need to generate landscapes for? The "best" softeware is going to be determined by what you need your final product to be.
Not that I have an awful lot of experience with landscape-generating software. At work we build our landscapes in an in-house worldbuilder program. But in cases where we want mountains extending off into the distance, I also use a program called World Machine to generate random mountains, and an intermediary program called Leveller to combine those mountains with the hand-built landscape already in our game.
I think you are awesome, and I wish you the best in your endeavors, but I am tired of repeating myself, I am very busy with my new baby, and I am no longer a regular participant here, so please do not contact me to ask for advice on your career or education. All of the advice that I have to offer can already be found in the following links. Thank you.
I don't know if this is exactly what you want but SketchUp is freckin amazing for building levels quickly and then exporting it to 3dsmax or Maya for tweeking and refining. It's pretty basic and geared towards industrial designers but with sketchup you can build a rough industrial level/scene in about five minutes. I have used it a few times building levels for the source engine and it's soooo awesome.