Just starting the shift from Bryce to Carrara I have to say it's the first program I've felt 'at home' in since Bryce.  I've tried and failed at C4D for instance. 

Things that would tempt me to stick with Bryce...  I have enough knowledge of the program to be able to make a scene pretty fast so going back to being a beginner can be a trial.  I have lots of things stored for Bryce that can speed things up.  Masses of free presets and skies and things in Bryce.

Some of those are also reasons why I think Bryce is a good place to start. There is so much free stuff to get you going and it is a bit of a cult software so that you can find really experienced users able to help you out with almost anything you want to do.

But... things that are really going for Carrara now I've started learning it (working through Mark Bremmer's tuts at VTC as we speak ;) ) are like having Bryce then adding on all the things you wish Bryce would do like the four screen view, the surface distribution, displacement mapping (oh how I drool to think of playing with displacement maps at last as my C4D was before effective implementation of that).  I'm sure there will be much more to get me going as I learn.  When I look at the wishlist for Bryce 7 I am sometimes thinking 'why ask for that in Bryce 7 when you could by Carrara now?' :)

Kathy