Having contributed to both (nothing major but not trivial one-liners either), my feeling is GCC definitely has a higher quality codebase and a more rigorous rev

Having contributed to both (nothing major but not trivial one-liners either), my feeling is GCC definitely has a higher quality codebase and a more rigorous review process. While the latter doesn't always translate to the ease of contribution, I found that if you are persistent enough, your patches to GCC will be reviewed. On the other hand, I had my patches to LLVM ignored forever. Just my 2c based on experience.