And theoretically clang has better ASM output in some cases I say theoretically, because it's been shown that GCC's "worse" ASM performs better; I'm not really an architecture aficionad, so I can't comment as to why that is.
Also, it's been a few years now since I did C/C++. So, maybe these are no longer the case.
Anyway, I've kinda pointed out what I like about clang over gcc, but I'd be curious what you prefer in gcc.