I've decided to stop my usual dithering over decisions and just dive in. Today I'm taking the plunge with Nirvana after test-driving it and Nozbe as well.
Both are good. Ultimately my decision came down to this: I feel Nozbe has better features but Nirvana offers a more faithful GTD implementation.
It's true I'll be giving up the Siri and Drafts integration I have with Evernote today, but I'll be gaining a way to link projects to next actions. After several years of going without it, I'm at a point where I've realized I can really use that feature.
And I can use Siri to dictate and send an email to Nirvana. That's as good as a direct Siri integration as far as I'm concerned.
While I do have reservations about Nirvana's slow pace of development -- from reading reviews it appears they took months to support the iPhone X which left some users high and dry -- if this doesn't work for me it's not like I can't switch.
@Longstreet can say that I've come over to the dark side (or the light side, depending on your point of view).
@TesTeq and I are likely headed for that epic wrestling match in the Jell-O pit.