LLVM seems to have better defaults for branch-y compiler code, but GCC has a lot of tricks up its sleeve that LLVM hasn't got.
FWIW though I think GCC is really playing with fire when it comes to it's future - the mailing list approach to development deters new contributors, the testing infrastructure is quite arcane, etc.
GCC should be an aspirational tool that people want to contribute to but aside from a few core contributors it feels like its basically on life support in some regards. And I say that as someone who actively tries to use it.
Its core competencies are pretty good but it's (mostly stallman, to be blunt) legacy has made it very brittle at its extremities e.g. LTO explodes on me way too often.
And LLVM is better? At the start of last year I found and fixed a small bug in LLVM[1]. I submitted the fix via their Phabricator instance and it was approved by project members after a few days. As per the contributor guide, I then asked for a project member to commit my patch to the LLVM repository. This is because in Phabricator there does not appear to be an automatic way to commit approved changes. A project member has to manually take the patch and apply it.
A few weeks ago I tried to see what happened to my patch and found that it had never been applied. So basically my work and that of the reviewers was simply lost because of their infrastructure.