I almost posted this in the Bryce Forum, glad I saw you posted here too. I don't go in for app. bashing and don't want to cause any conflicts. Unfortunately, it seems that comparing applications isn't looked on very kindly here at Renderosity.

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I'd go with Carrara, if it is between those two apps., mainly because of the Poser support via Transposer plugin. Bryce also does not have wind effects or physics, so it is difficult to create a realistic animation in an outdoor setting.
I personally had some trouble with the interface, but it only takes time. Many users really like the C5 interface; that is a personal preference.

Friends don't let friends use booleans.