"I'm assuming the learning curve is fairly the same" - This would probably be an incorrect assumption, at least if you are talking about the programs as a whole. Carrara has a lot more capabilties, tools and functions, some of which rival the output of the "Pro" softwares you mentioned.  If you are talking about  "Carrara Basics", and not Carrara5 standard, or Pro, the comparison and learning curve would be much closer. In the following I will discuss the capabilities of the standard, or Pro versions of Carrara.
     Since I use both Bryce and Carrara, I have no "axe to grind". You can build superb landscapes in both apps, but due to Carrara5's advantage with its surface replicator I'd have to give it the nod as far as creating large,(huge!) landscape areas. I've populated terrains with tens of thousands of randomly distributed trees with little extra memory overhead.  You can even replicate and tile terrains to have landscapes extending effortlessly to the horizon.
   You can control the distribution of trees, grasses, weeds, rocks or other objects with non-visible greyscale maps or materials that you can apply to your terrains. The ability to use animated displacement maps in Carrara also makes it possible to make convincing streams, rivers, lava, or mudflows.
        Carrara supports wind animation for its trees, and an available plug-in called "Anything Grows" will let you grow and add wind animation to fields of  grasses and flowers.
Carrara also supports particles, forces, and physics so you can make convincing animated smoke, drifting leaves,fountains, explosions, etc.  Carrara has excellent animated volumetric clouds as well and quite frankly, the rendering is much faster.
  Sometimes though, I just open up Bryce instead because it is so easy to use, and I still love it.