Currently I won’t upgrade, I have a Fusion Drive which isn’t supported by APFS yet. I’m not desperate to upgrade for that, HPFS+ has never hurt me yet, I keep a reasonable backup schedule, my source control is backed up.
I waited until last month to upgrade to Sierra, I was working just fine on Mavericks, and only upgraded because Xcode (UGH!) required it. So my advice is usually very conservative: Wait until you absolutely have to.
That said, there’s new stuff that is interesting in High Sierra: VR and new image file formats. So I’ll likely upgrade sooner, once I see fusion drives supported and hear no more horror stories.
On a side & musical note, I’m already super tired of the California theme. The other 49 states and hundreds of other countries don’t like you that much, Cali.