what format is better to export from blender to unity ? 
I would recommend FBX type
Unity support a variety of file types, you can see them all here Unity - Manual: Model file formats
Unity supports importing Blender files directly as you can see in the documentation.
Personally I would recommend exporting as FBX files as it the majority of 3D programs support it. Please be aware that when exporting files from blender, the model might appear rotated and differently sized due to differences in coordinate system and scaling. You should find a guide to ensure your blender environment is set up to match Unity.