Wow, what a great topic and dangerous question! Like asking whats the best beer.
First and foremost I bought my fattie explicitly based on price. It was a used fattie right here on this forum, didn't know too much about em other than I rode one once (pug) and smiled. It did not matter what make/model, cuz it was cheeeep and fatbike don't give a ****. Its a Mukluk.
Learned a bit about fatties since then, mostly that they make me smile every time and they go EVERYWHERE. I love my Salsa. As a jarhead with that Marine Corps drill in my head, I like things covered and aligned, squared away, even and balanced. Surly Pugs and Moonlanders with the standard width 135mm rear end was meaningful probably few years ago, but the offset non-symmetrical hubs & wheels don't fit in my brains realm of normal order. Not that there are problems, its just a slight OCD thing. The Mukluk (and many many others) 170mm symmetrical rear ends are a 'standard' nowadays with more than adequate component configurations available. Its wider, but even, centered and balanced. And its aluminum. And its got alternator dropouts. Has the braze-ons. And to my knowledge its not had any weld-breaking problems.
In the $1k-2k range, if I was to buy another fattie, it would be a Mukluk. If I had disposable income, I'd look far NW to Alaskan frontier and some of those premium machines.
With all that said, I'm a fan but don't own Surly bikes. I think Surly & Salsa are both owned by QBP. I'd love to have a Surly disc trucker. The Krampus is a Bikepacking machine, or the ECR Steve-o mentioned. But o' course those are not Fatties that go EVERYWHERE.
Good Luck in your decision. As many have said, you'll be happy no matter what make/model you procure. If you think gravel roads are fun, wait until you stomp some trashgrounds on a fattie.