I've become a fan of Generatepress lately. It's newest version cleaned out all floats for layout and uses flex and grid, it gives good HTML that is reasonably lean.
I chose it because it was the fastest, lightest theme I could find that was not pared down to the barebones. I am not a stickler for HTML validation. Once you add in plugins and such, it can be a real challenge. However, I am a stickler for lean, well-formed HTML and sites that do well on Pagespeed, Lighthouse and the like. I've done two Generatepress sites in the last two months and am happy with the balance between being nice looking and having decent performance. In both cases, it is the images and the plugins that are the performance killers, not the theme.
