Volume One would collect ten Fantastic Four stories from the pages of What If?. The story from #31 would be the FF back-up, noted on the bottom of the cover. The story from #37 would be the Thing story only. I'd use the cover of What If? (1977) #1 as the cover to the TPB, because it's a great pic of the Fantastic Five busting out of the cover, almost like all the FF stories in the TPB were busting out to meet you.
I think all 9 of the stories in Volume Two are great, including a couple about the New Fantastic Four, but I think the cover should show a recognizable picture of the Fantastic Four most people are familiar with. For that reason, #27, 30, 35, 89 or 109 are candidates. Overall, I think since I picked the Fantastic Five cover for Volume 1, I'd go with the Fantastic Five here as well, and use the cover of #35 as the cover to this TPB.
Would you buy it? Let me know in the comments, and thanks for reading.