Contrarian view: Democrats, because even with the various trends in their favor, they now have to win by almost 10 to control anything.
If you're talking about the House popular vote, it's not necessarily 10 and it wouldn't always be 10. There are some estimates that say Democrats could flip the House with as few as 5-6 points, although the more common number is 7. I've only seen one analysis mention >= 10 before, and I still think that is much too high.
Also, this high number is what it would take to
flip the chamber, not maintain an existing majority. The incumbency advantage accounts for some of that larger margin, which would be reversed if Democrats won, say, a 230 majority. Then it might be the case that Democrats could hold the House with a smaller margin.
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