Learning curve vs. functionality goes like this with these programs... at least, as I see it:
Well, first a list of comparable programs and their availability/cost:
Two are free: Blender and SketchUp. But SketchUp is rather limited unless you want the professional version, which might cost quite a bit. More on that in a second.
AC3D is inherently not free. The demo is free to try. The licence, however, is not very expensive AT ALL. I think current versions will cost a bit less than $80 USD. This is not at all too much to spend on a CAD program. Most of the plug-ins are free (all the ones I use are) and the program continually gets new features. The licence lasts for a while in terms of upgrades, so if a new version comes out, it won't cost you to upgrade. And if the licence is old, upgrading it is pretty cheap in comparison.
SketchUp Pro is like... $400 USD I believe? A student licence is around $50 if I'm not mistaken, but it only lasts for so long.
Immediate user reaction to the program:
SketchUp gets the title for easiest to start with. Draw a shape and grab the extrude tool. Cool, I made a box! Going farther than that, SketchUp starts to get tricky. It's certainly workable, as I've seen some very impressive SketchUp (free version) models. But to do those things, you actually need to be able to get a hang of the program.
AC3D is great. The interface is intuitive and the functions make sense. And you have a great many of them. When there's a problem, reading through the manual (which comes with the application) usually will help you out. In short, it's easy to use while it doesn't have the immediate modeling limitations SketchUp does. If you need to render something, Download a free rendering program called POV-Ray. AC3D is designed to use it, too.
Blender is free and uses free elements to run it. The latest versions need Python 2.6... just go to python.org and load 'er up! Next, get Blender. From there, you'll probably be frustrated until you get help. Most of the functions are hotkey based and the UI is not descriptive at all. If you get past those limitations... I've seen some remarkable work done with the program. Hooray for open source! The program has a built-in rendering engine, a programming interface, etc., etc. I'll need to really sit down and learn the application someday, but until then I'll be happy using it to import .dae files from PCS2 and convert them to .ac files.
If you're cheap... AC3D is not too bad. If you're cheap as in I-just-spent-$500-on-textbooks-and can't-afford-squat, go with SketchUp or Blender. I'd choose Blender over SketchUp despite its frustrating UI.
