"If there was one best tire, nobody else would make tires."
So do you change tires on route ? When I did LEJOG there was a huge difference between so called canal paths for instance some were like mountain bike tracks especially during 10 days of heavy rain & other Tarmac & I had a happy medium of tire set up that I was happy with . I just wondered what that would be on a Thorn Nomad MK2 as the Dureme won't be available .
So, if you are looking for a Dureme, a Marathon with Greenguard or a Mondial might be alternatives.
No, I do not bring a bunch of tires and change them on a trip. On my Sherpa, if the route is mostly paved I am using a Schwalbe Marathon (with Greenguard) in 40mm width. If I am on a trip with mostly gravel I am using 50mm width Marathon Extremes (discontinued) or Duremes. The Extremes have a more aggressive tread, the Duremes have a more pavement oriented tread. On that bike, I am picking from those three options. And I should point out that this assumes I am hauling my camping gear on the bike. If I was going somewhere to ride an unladen bike, I would probably pick a 700c bike instead.
I make that plan in advance based on where the bike tour will be. And I am also chosing a bike based on how heavily loaded the bike will be. My other bikes, I am more likely to have a shorter list of choices, as I have used my Sherpa on a wider range of road surfaces than my other bikes.
For a loaded tour, on my Nomad Mk II, I use 57mm wide Marathon Extremes, but I was thinking on the last tour I did with that bike that a 55mm Dureme might have made more sense up front, I have one of those that I could have used. Up front the aggressive tread of the Extreme was overkill.
Since I have not bought tires for these bikes for several years, I can't say what I would buy today because I do not know what is available today.
If I carry a spare tire on a trip, it generally is not a replacement for a tire I am using, instead it is a light weight tire with minimal tread that I would use to get to a bike shop where I can get a better replacement tire. Thus, my spare would be lighter and smaller in the bottom of a pannier.