All depends. For a longish journey (say 100-200 miles) 8000-10000 unless winds dictate otherwise. For a local journey, 2500-4500 - remember we are surrounded by mountains here. In the helicopter, 1000 or 1500 AGL unless terrain dictates otherwise.
For REALLY long journeys, higher can be better, also when flying across the desert in the summer. I have done a couple of trips at FL200 to catch the winds up there. But it's a long time since I've been up that high.