Primstar-2 is mainly focussed on modelling of sculpted prims + terrain support. Primstar-2 has very limited support for mesh. That is: the Sculpty base objects can be used as mesh template objects. The advantage of doing this is that the sculpty base objects already have a very simple even spaced UV map. This can possibly help you making simple textures.
Avastar-1 is mainly focussed on animating of mesh based characters (Avatars). Avastar also has good support for mesh based character modelling and attachment creations. Avastar comes with its own Collada exporter. The advantage of this: The Avastar Collada Exporter is optimized for usage with Second Life and it creates the most acurate results (An object model appears in blender exactly like it appears in Second Life). However note that textured objects may look very different, because Second Life lacks a couple of important texture features (normal maps, materials…) hence textures always look much better in Blender than in SL.
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