I’m using Blender a lot, for my mesh modeling. I’m not saying the SL prim system is not good, I like it a lot, but with Blender I have more freedom in building complex meshes. There are some simple things we can’t do just with prims, or… with “some” prims. Think to a simple bottle, in example a wine bottle: with prims you can fail in doing it, or you will need a lot of prims. Indeed, on the marketplace you will find a lot of simple objects (like bottles) with a high Land Impact. With a mesh bottle, designed in Blender, you will have a nice bottle with a Land Impact of 1 prim!
For my experience, there are some things requiring your attention, in Blender.
First of all, the dimensions. When you export from Blender to SL, you will find anything doubled in size. In example, if in Blender you build a cube with a edge lenght of 1m, in SL you will see a edge length of 2m. I solved this building things at half size. The important is make two things.
1) before exporting, apply all tranforms: location, rotation and scale
2) export as collada, but select the tab “Arm” and check the box “Export to SL/OpenSim”.
After this, import it as model in SL, and just rez it. You will have a prim but you can’t walk inside it, so this is not good for a house, or similar. In order to do this, you will need upload physics too, and set to “Prim” the “physics form type”, but for this you can find some good manuals and how to on the Internet.