It looks like there is very little 3d modeling done in those two images. The second one may just be a hand drawing with photoshop trees, texture and tone. For this, making a sketchup model, printing it, drawing over it to achieve correct line weights and then using photoshop for the rest is the easiest method. I’d say you’ll be best to learn both programs, more or less. Rhino is another program that is far better than sketchup and along the same lines as 3dmax, but it is easier to use. It’s main drawback is the lack of a terrain-from-contours modeling tool. In the end, you’ll want to use certain programs for certain tasks. Don’t limit yourself to one, especially not just sketchup.