I've heard that Yamahas are mostly underrated. I've heard basically consistently great things about Nathan East's sig basses through the years, as well as Billy's, John Patitucci's, Michael Anthony's, and others. The only sig models that I've heard mixed reviews on, were the old John Myung basses.
Btw, I heard a cover band open for my band, and the bass player had an Attitude...it sounded almost exactly like the Billy himself, tone-wise. The cover band player was pretty decent, so even more so like Billy's sound. I tech'd for Billy, back in '06 for the first Bx3 tour, and his bass was solid as a rock. We had to superglue the brass nut back on once, but Billy beats the crap out of his basses (and they can take it), so I wasn't surprised.
Not to hijack the thread, as this photo was from our first dinner, before the first show at Shank Hall in Milwaukee (yes, the same from Spinal tap). It was a German place, called Mader's. I'm second from the left.