Well, I've never used Bryce but a few years back I played around with both Terragen and World Machine. Terragen works off the premise of a greyscale elevation map. World Machine has a whole flow chart that you lay out to affect the terrain. Both have great automatic algorithms for creating erosion. That might be some place to begin. For me, Terragen was more intuitive whereas World Machine took a bit more effort in learning how to work with it. Both created some great land maps, especially if the height field was generated in World Machine and then imported to Terragen (though this is just a bonus not a requirement).