As another former, happy user of 28mm Supremes I'd recommend GP 4 Seasons for their combination of resistance, weight, speed and ease of removal/fitting. I did most of my RRTY on them and, according to my spreadsheet, they lasted 8600 miles with 2 punctures each. One tyre had to be replaced when a huge piece of toughened glass took a chunk out of the tread. The glass would probably have done in a Marathon Plus ....
I'm currently rocking a pair of 32mm Gravelking SKs on my go to bike (On One Dirty Disco) and I can't praise them enough. The rear has done 1750 miles and I haven't had to remove it yet (IYSWIM). The front tyre replaced my last 28mm Supreme; it's only done 350 miles but I love them for being good on road and off. Despite their pronounced tread, they don't feel any slower on road than Supremes.
Another alternative is the standard Gravelking in 26mm (they seem to come up a little bigger): 3300 miles so far and 1 puncture, that on a thorn strewn ride that saw six out of eight of us succumb either on the day or the next morning. Luckily for me, my Supreme/GK SK combo came through unscathed. Affected tyres included an M+, a Marathon Supreme, a Schwalbe One, a GP4 Seasons and a Clement USH. We fixed the Gravelking in the pub at the lunch stop, it resisted that far; lever to get off, thumbs to replace.
tl;dr GP4 Seasons or Gravelking 26 or 28mm but don't rule out Gravelking SK.
As ever, ask 10 cyclists about tyres and you'll get 11 opinions ...........