I’ve read both Catton and Foote - 3 volumes each.
Major differences are that Catton was an historian and his sympathies at least tilted towards the North. Foote was primarily a novelist (that’s why his books are titled - The Civil War: A Narrative) and his sympathies are more in line with the South.
They’re both excellent however - albeit it takes a while to make it all the way through either work.
I read Killer Angels by Michael Shaara. You are right. It is the best Civil War book I ever read. It is a historical novel. It won Pulitzer Prize for best fiction in 1975. Every American should read it. Was it Jubal Early who failed to occupy the Little Round top on this date June 30 in 1863? He let his Confederate troops rest while the 20th Maine occupied that high ground. The rest is history.
Just finished reading Foote for the second time. His sympathies fairly obviously shift more towards the North as the books progress. He even explains why in the introduction to the last volume.
It took him 20 years to write the darn thing and the racist southern politicians of the 50s and 60s, who claimed to be upholding the principles of the CSA, soured him to some extent on the original enterprise itself.