All space anime is mecha regardless as to whether or not it has giant robots in it. The term "mecha" is just short for "mechanical" and any anime that goes out of its way to show off its mechanical designs may be considered mecha.>>2397
Well it's clear that you just wanted to start a Legend of the Galactic Heroes thread. Nothing really beats that as far as space operas go. Aside from maybe the Leijiverse, you'll find hard contenders.